The Mexican War and Imperialism by Other Means
Analogous to biological cells, which will multiply and grow unless inhibited by contact with others, the United States, lacking a contravening contiguous power that could match its own and no different from any other human polity in history, spread as far and wide as it could. Like the Pilgrims and conquistadors before them, Americans expanded for a variety of reasons: for gold and other kinds of perceived economic opportunities, to escape religious persecution or other social tensions, land hunger, to civilize as they saw fit, and probably also for the sheer sense of freedom and self-reliance that risky adventure provides. As is usual in human history, the desires and needs of those in the way generally ranked very low.
Soon, with the continent's frontier exhausted, Americans would take to the seas in what is erroneously considered the birth of American imperialism (recall the "salt-water fallacy" mentioned earlier). We have always been "imperial" -- that is, expansionist -- whether "we" refers "Americans" or, indeed, "human beings." That our nation has constructed an ideology of manifest destiny based on American Exceptionalism is itself hardly exceptional in human history. It's not even particularly American: just about every society thinks itself exceptional and destined to grasp the mantle of as much dominion as possible. It is only in the twentieth century, following a near-suicidal world war and the rise of weapons of truly mass destruction, that our species has haltingly attempted to change the rules of existence laid down since the Pleistocene.
The Conquest of Mexico and the Purchase of Oregon
So, Mexico. Recall that after winning independence from Spain in 1821, Mexico's territory included all of the current southwest quarter of the United States. Texas itself, long settled by Americans despite Mexican rule, declared independence from Mexico in 1836 and a decade later became one of the United States. As for the rest, James Polk offered a purchase. Mexico refused. So, a military cross-border provocation was arranged and Mexican resistance was deemed an invasion that American honor must answer. In effect, the United States had launched a war of conquest because its neighbor had declined to sell nearly half of its territory. Many at the time, like Lincoln and Thoreau, recognized the travesty. Thoreau wrote (and more or less invented the tactic of) Civil Disobedience, in which he justified an individual's moral right and duty to resist immoral acts by the government, a sort of "personal nullification" that in this case took the form of a refusal to pay taxes, and which would, in many other forms, have massive global impact through later practitioners like Martin Luther King and Mahatma Gandhi. It's worth pausing to note that in America both flimsily justified imperial wars and principled anti-war protest are of equal venerability.
The Americans crushed Mexican forces, took Mexico City, and forced an advantageous peace that retroactively legalized the annexation of Texas while also adding today's New Mexico, Arizona, California, Nevada, and Utah -- the Mexican Cession for which they were paid $15 million. North of the Cession's territories had lain disputed Oregon, which constituted the current northwest quarter of the United States and had via its famous Trail already been filled with American settlers. Oregon was dually governed with Britain, our main overseas rival, and a warlike resolution to this situation had also been on many a mind, but Polk had managed to work out another longitudinal deal by which Britain took what lay north of the 49th parallel and the United States took what lay south. Adding in the small Gadsen Purchase in the southwest and the purchase of Alaska from Russia in 1867, the current continental borders of the United States were set.
Be Careful What You Wish For: New Territories Heighten Sectional Tensions
All this territory constituted a giant safety valve for internal pressures of all kinds, from religious persecution (of, for example, Mormons) to lack of economic opportunity. However, the newly acquired southwest immediately heightened the issue of slavery: how many states would be carved out of this vast territory, and would they be slave or free? The ink on the Mexican War settlement was hardly dry before the Wilmot Proviso insisted upon free labor in all newly acquired lands. Party loyalty instantly evaporated; Whig or Democrat, northerners supported it and southerners did not. In short, the Mexican Cession had blown up the Missouri Compromise. It's one thing to divide a relatively small territory and consider the rest in theory; it's quite another to have conquered a vast territory and have to live with the Missouri Compromise in reality.
The Free-Soil Movement brought to bear another anti-slavery argument, that whatever one thought of slavery, its spread would necessarily undercut the wages of free labor. The movement became a political party, one that would flow into the new Second Republican party of Lincoln. Northern abolitionism, sometimes encouraging slave escapes via the Underground Railroad and welcoming violent resistance to slavery (such as those of Nat Turner in the 1830s and much later of John Brown at Harper's Ferry in 1859) grew in power, terrifying Southern plantation owners who dominated both slaves and poor whites and increasingly justified slavery on quasi-biological grounds, bolstering longstanding religious and cultural justifications.
Added into the volatile political mix was a massive influx into the North of mostly Irish and German Catholic immigrants which caused a nativist reaction -- the Know-Nothings. These nativists tended to ally themselves with southern Democrats who claimed to protect "pure" Americans from not only those who would impose free blacks on whites, to say nothing of the blacks themselves, but also what were seen as a never-ending invasion foreign Catholic hordes. Virtually all Americans, of course, were in agreement that Indians were simply to be ethnically cleansed.
Further compromises arose but to little avail. The Compromise of 1850 ensured that California would be free, the slave trade but not slavery itself abolished in the nation's capitol, fugitive slaves would diligently be returned to their owners, and the status of the remaining Mexican territories would be left up to referendum -- the idea of popular sovereignty later championed by Stephen Douglas. For a short time, party loyalty returned and sectional loyalty receded. But in 1854, the Kansas-Nebraska Act formally repealed the Missouri Compromise, opening up lands not part of the Cession and formerly deemed forever free to the possibility of slavery. Its main accomplishment, aside from launching a civil war in Kansas, was to destroy the Democratic Party. Much of its northern wing united with Free Soilers and the northern remnants of a Whig Party, itself incapable of holding together in the face of the crisis, becoming the Second Republican Party. (Henceforth, we will refer to this simply as the Republican Party.) The Dred Scott Case of 1857 didn't help matters: it ruled that blacks could never be citizens of the United States and thus permanently lacked standing to sue anyone for any reason. Moreover, it undermined not only popular sovereignty but also pretty much the raison d'etre of the Republican Party by declaring, needlessly, that slavery was constitutional, period, and therefore that no act of Congress, let alone that of any state legislature, could change that fact.
Parties now almost entirely reflected sectional interests: a Republican North and a Democratic South. If politics is war by other means, those other means were soon exhausted. In 1860, the South declared that if the Republican Lincoln was to win the presidency, they would leave. He won; the South left.
The Civil War: The First Modern War
The South needed to strike fast and hard and win quickly since the North had far greater manpower and a much larger manufacturing base. Alternatively, if the South could attract a foreign power to its side, a la the revolutionary colonies did with France, then it might also force a victory. The South nearly pulled it off, initially having by far the better generalship. However, the North held on long enough to bring its economic and diplomatic advantages fully to bar. By the Emancipation Proclamation of January 1863, which explicitly added the destruction of slavery (at least in captured territory) to the Union's war aims, and the Gettysburg Address, which followed in November of that year, the North had ensured that European powers, who had large antislavery constituencies, would not intervene. As areas of the South were taken (and even before), black slaves fled to the North often to join all-black units in the Union Army to fight against their former masters. By mid-1863's battles of Gettysburg and Vicksburg, Lincoln's generals had won enough victories on the field to further warn off potential foreign intervention. In January, 1865, before the war was even over, the Congress approved of the Thirteenth Amendment, which outlawed slavery throughout the entire nation.
One other reason the North won was that it eventually engaged in total war, the first power to do so in world history but hardly the last. Total war meant full mobilization of the entire society for victory while leaving untouched no aspect of the opponent's society. For the first time, the North instituted a draft that met with often violent resistance (especially in New York City). It completely destroyed the South's infrastructure, as exemplified by Sherman's march to the sea. Both sides housed prisoners of war in what were essentially concentration camps, the most famous being the South's Andersonville prison. Mechanized warfare in the form massive railroad-based artillery and ironclad ships debuted under the watchful eyes of European observers. As with World War I, the combination of modern weapons, the desperation of total war, and somewhat out-of-date warfighting tactics and strategies yielded mass death, especially during the last year of so of the war. Lincoln declared that nothing short of unconditional surrender would suffice while he ruled as a near-dictator, suspending habeas corpus and closing newspapers. However, there were limits to what power Lincoln would claim in wartime: the Democrats in the North were not disbanded, and a presidential election that Lincoln might well have lost took place in 1864.
The total war that the Civil War became not only reunited the country but also transformed the it into a new, powerful, centralized nation-state. Despite demobilization, the United States was never again to resemble the decentralized agrarian republic it had once been. The war was partially financed in the North via the first income tax in American history. State-based currencies were finally replaced by Federal notes. The nation was further knit together via the Homestead Act, which offered free land to Western settlers; the Land Grant College Act, which gave federal help to states to create agricultural colleges; and the launching of the Transcontinental Railroad, finally completed in 1869.
Reconstruction and its Deconstruction
The first phase is known as Presidential Reconstruction, beginning with Lincoln and continuing with Johnson and ending in 1867. Thereafter came Congressional or Radical Reconstruction, which fell apart in the aftermath of the contested presidential election of 1876. Neither wave of reconstruction changed the economic basis of the South, aside from the formal banning of slavery. The South was part of the Union and slavery was outlawed, to be sure, but the South ran its own affairs with no Union army threat, and slavery had been virtually reinstated via a harsh serfdom for nearly all blacks and most poor whites.
Presidential reconstruction could be said to have started in an ad hoc fashion during the war as generals took back sections of the South. It was further advanced by the Emancipation Proclamation, the Thirteenth Amendment, and the establishment of a short-lived Freedman's Bureau (1865-1870) which directed private funds toward the building of schools and hospitals for southern blacks. Lincoln was assassinated shortly after the war's end. This left the work of reconstruction to Andrew Johnson who, like Lincoln, refused to consider using the Union victory to reshape the economic basis of Southern life. Thus, slavery was soon replaced by sharecropping, a feudal system that also drew in poor whites. Under this system, a poor black or white family could rent part of a plantation, earning through the rent via a portion of what was grown. For those poor farmers who could access finance, this system was augmented by the crop lein, usually with high interest rates, in which a portion of future crops served as collateral. Not until the 1930s would much racial or economic change begin to come to the South. Much turned on the North's refusal to break up and redistribute the large plantations, a step considered too radical for even the Radical Republicans.
Johnson also instituted a blanket pardon of all Confederates willing to take an oath of loyalty, including, later, wealthy and powerful Confederates who received personal pardons rather than any punishment, let alone dispossession for the benefit of either blacks or poor whites. Thus, and despite unconditional surrender, Johnson reconstituted not only the power structure of the South but also many of its (surviving) personnel. Though blacks were elected to state legislatures, the white power structure dominated, and soon passed Black Codes, the beginning of Jim Crow, that attempted to control as much of black life as possible: blacks were prevented from voting, serving on juries, and testifying against whites. Moreover, some states ruled that any black who refused to sign usually serf-like annual work contracts was eligible for re-enslavement, as were, in some states and under some circumstances, the children of blacks. Other states banned blacks from owning land or participating in certain occupations. Within a year of war's end, the Ku Klux Klan, an armed terrorist organization (and sometimes considered a harbinger of twentieth-century fascist movements), was also fighting to reinstate as much white power as it could possibly get away with until in 1872 Grant crushed its first instantiation. It would return.
Growing increasingly frustrated with Johnson, Republicans impeached him (for refusing to follow a law not directly related to Reconstruction), but fell one Senate vote short of conviction. Fatally weakened, Johnson took a back seat to the Republicans in Congress. They had already passed the Reconstruction Act in 1867 over Johnson's veto, a law that divided the South into five military districts, called for the creation of new state governments, and guaranteed the vote for blacks. The Fourteenth Amendment of 1868 made citizens of all people born in the US; the Fifteenth Amendment of 1870 enshrined in the Constitution the Reconstruction Act's voting rights -- for men, that is, a feature not lost on the feminist movement segments of which fought against the Fifteenth on the basis of women's exclusion. Periodically, southern terror attacks would erupt only to be put down by Northern troops. As soon as that will failed, so too did Reconstruction. And that was the rub: having lost to the North in a war of attrition, the South would soon win the Reconstruction battle through an ongoing war of political attrition, though violence played a key role.
Liberal Republicans, as they came to be known, grew disgusted with the undeniably corrupt Grant administration and turned to Democrats for allies. By the depression of 1873, Northerners were growing increasingly preoccupied with non-Southern problems. In 1875 and facing a Democratic congress elected in 1874, Grant did not respond to yet another uprising in the south against black voting rights, which had temporarily populated state and even federal legislatures with black parliamentarians. In the South itself, by a variety of means including violence, Democrats were suppressing the black vote and thus undermining Republican representation. One by one, Southern states flipped Democratic. By the contested presidential election of 1876, the first (but not the last) decided outside the polls, an election noted for mass cheating on both sides, the Republicans were more than willing to end Reconstruction as part of a deal (the Bargain of 1877) that handed the presidency to the Republican candidate, Rutherford B. Hayes. Soon after becoming president, Hayes ordered federal troops back into their barracks throughout the South, ending the only possible force that could guarantee rights to southern blacks.