The powerful new "Lincoln" movie is drawing large crowds. Almost the entire drama occurs in January 1865, after President Lincoln's re-election, as the Civil War nears an end. The legendary president pursues an obsessive goal: to pass the 13th constitutional amendment and wipe out slavery completely, as his Emancipation Proclamation previously attempted partially.

The U.S. Senate, controlled by Lincoln progressives, approved the amendment easily -- but conservatives in the House fought fiercely against ending human bondage. Lincoln lacked enough House votes. Intense conniving, threats, semi-bribery and political duplicity ensued for days, until the White House finally won a tiny two-vote victory. Jubilation erupted among America's liberals of that day.

The movie vividly shows the sort of struggle that happens time after time, publicly and covertly, as America engages in never-ending ideological showdowns. These U.S. conflicts keep changing as circumstances evolve, year after year, century after century -- yet the battle is eternal, always pitting progressive reform crusaders against conservatives resisting change.

This clash of worldviews dates back at least until colonial days when conservative American Tories wanted to remain loyal to England's king, while radical reformers sought to break free and launch the world's first modern democracy.

In many ways, America's history is a tale of liberals defeating conservatives. Some examples:

* Conservatives opposed women's right to vote, but progressives finally won this landmark advance in human rights.

* Conservatives fought against birth control, but two liberal victories in the U.S. Supreme Court finally allowed couples to limit pregnancy in the privacy of their bedrooms.

* Conservatives resisted Social Security and other New Deal "safety net" protections for struggling families, but liberals won those historic advances.

* Conservatives opposed equality for blacks, but the civil rights movement gradually triumphed.

* Conservatives battled Medicare, Medicaid, ObamaCare and other health guarantees, but liberals secured these safeguards against disease and injury.

* Conservatives rail against gay equality, but a liberal tide slowly is erasing prejudice against this minority.

Everything has changed since Lincoln pulled strings to defeat slavery -- yet America's underlying struggle endlessly re-emerges in new forms. As long as progressives keep winning, Americans will continue to gain better lives.