The American patriots who flung crates of imported tea into Boston Harbor on Dec. 16, 1773 were acting against their countrymen’s economic interest. The Tea Act, adopted by the British Parliament, allowed direct shipping of the East India Company???s surplus tea to North America, bypassing middlemen in London and reducing the price in the colonies. But that price still included a tax, enacted by a parliament in which the Americans were not represented. To purchase the tea would violate the principle of ???no taxation without representation.??? And so the Sons of Liberty chucked it into the water. Recall this history as you consider today???s Tea Party ??? and other zealous movements at the other end of the ideological spectrum. Regardless of whether one sympathizes with the Tea Party, MoveOn.org, or none of the above, it should be possible to recognize what they have in common: an attitude. And it is characteristically American. Call it the spirit of anti-compromise. We Americans like to think of ourselves as a pragmatic nation. Problem-solving and compromise have a long history in American politics. So, too, however, do extremism and polarization. As the Boston Tea Party itself illustrates, this country was born in a fit of uncompromising zeal. No less a patriot than Benjamin Franklin was horrified by the Tea Party. From his vantage point in England, where he was attempting to negotiate with King George III???s government, the destruction of the tea struck Franklin as an ???act of violent injustice on our part.??? The Philadelphian spoke for many moderate colonists. But the Sons of Liberty were more intent on making a point than solving problems. Between their uncompromising attitude and that of the Crown, the situation became polarized. Franklin and other moderates had to choose sides. The Revolution was on. Today, we admire the American revolutionaries, and subsequent uncompromising movements. But don???t forget: The victors write history. If the South had won the Civil War, what would our schoolchildren be taught about the abolitionists today? Some in the antislavery movement were as extreme, in their way, as the Southern ???fire-eaters.??? We tend to think of the secessionists as resisting federal authority during the run-up to Fort Sumter. But the antislavery side had its moments of nullification as well. In 1851, a Boston crowd broke into a federal courthouse to free ???Shadrach,??? a black man being held there by U.S. marshals enforcing the Fugitive Slave Law. Abolitionist Theodore Parker declared this blatant defiance of Washington ???the most noble deed done in Boston since the destruction of the tea in 1773.??? I am not suggesting a moral equivalency between the anti-slavery and pro-slavery forces. But I am suggesting an attitudinal equivalency ??? one that has been played out repeatedly in our history, and that may play out again. If you think today???s discourse is vitriolic, open any history book and read the words ??? ???Judas,??? ???Traitor,??? ???diabolical??? — that Americans hurled at one another in the past. Indeed, if you think there???s something uniquely ugly about the contemporary Tea Party???s abusive rhetoric toward President Obama, check out this compendium of violent language aimed at President Bush a few years ago. But while political movements have embodied the spirit of anti-compromise, political parties have embodied the spirit of compromise. Whatever their names ??? Federalist, Whig, Democrat, Republican ??? the most successful American parties threw big tents over diverse interest groups and blurred lines of class, region and ideology. The parties co-opted extremes and ??? to be blunt about it — rescued politics from excesses of principle. ???Extremism in the defense of liberty is no vice,??? Barry Goldwater announced in 1964. He was declaring war not only on the moderate establishment of his own Republican party, and that of the Democrats, but also on the historic function of all American political parties: to make it possible for government to salve conflicts and solve problems. No doubt this has involved tradeoffs: Time and again, the parties have brokered peace at the expense of moral clarity. That is probably why the Missouri Compromise and the Compromise of 1850, each of which attempted to save the Union while sacrificing African American freedom, ultimately broke down ??? along with the Whigs and Jacksonian Democratic parties that cobbled them together. At other times, though, the parties have helped hold the country together. In the 1960s, for example, society was polarized, but, broadly speaking, the Republicans and Democrats were not. They hewed to the vital center. The parties incorporated zealous elements on both the right and left, and gradually moderated them. Today???s political dynamic is very different. Society is relatively moderate ??? 35 percent of voters think of themselves as independents, according to Gallup. But the parties are polarized; they have been captured by the extremes. As the November midterm election approaches, each of them is trying to fire up a ???base??? that is increasingly defined by ideology, and for which bipartisan compromise is inherently objectionable. President Obama protests that his health care policy is ???centrist,??? invoking past support for similar ideas from such hoary Republican stalwarts as Bob Dole. But for today???s Tea Party, the very invocation of Dole???s name, to the extent anyone still recognizes it, is a reason to oppose the plan. And it was only with the greatest of difficulty that Obama managed to bring his own party???s base around to support the bill; some are still furious that it lacks a public option. Perhaps if Scott Brown???s Tea Party-backed victory in Massachusetts had not enabled Obama to recast the issue as a stark matter of political survival, and a polarized battle between the people and the insurance companies, the Democratic base would not have cooperated. Whatever its ultimate impact on the health-care system, the bill is likely to further polarize the political system. The Democratic Party’s most conservative members (and they are not that conservative) have now been isolated and left exposed to defeat at the hands of Republican challengers in November. Whether House Democrats keep their majority or not, the caucus will be smaller and more purely liberal. By the same token, the Republican caucus will be bigger and more intensely conservative. This could actually be a positive development, if the ideological purge underway among Republicans and Democrats gives rise to a new party of outcast moderates. But don???t hold your breath. The situation reminds me of the second half of the 1850s, when the combined impact of the Fugitive Slave Law and the Kansas-Nebraska Act led to the breakdown of the old Whig-Jacksonian party system. I don???t think we are headed toward another civil war, of course. But I do expect more partisan vitriol and deadlock before this cycle of polarization ultimately runs its course. Given this country???s problems (economic stagnation, debt, terrorism), that scenario looks dangerous enough.