WASHINGTON (AP) — Turning the page on years of war and recession, President Barack Obama summoned a divided nation Monday to act with “passion and dedication” to broaden equality and prosperity at home, nurture democracy around the world and combat global warming as he embarked on a second term before a vast and cheering crowd that spilled down the historic National Mall.

“America’s possibilities are limitless, for we possess all the qualities that this world without boundaries demands,” the 44th president declared in his second inaugural address.

In a unity plea to politicians and the nation at large, he called for “collective action” to confront challenges and said, “Progress does not compel us to settle centuries-long debates about the role of government for all time — but it does require us to act in our time.”

Elected four years ago as America’s first black president, Obama spoke outside the Capitol after reciting the oath of office that all presidents have uttered since the nation’s founding.

The inauguration this year shared the day with Dr. Martin Luther King’s birthday holiday, and the president used a Bible that had belonged to the civil rights leader for the swearing-in, along with a second one that had been Abraham Lincoln’s. The president also paused inside the Capitol Rotunda to gaze at a dark bronze statue of King.

Outside, the Inaugural Parade took shape, a reflection of American musicality and diversity that featured military units, bands, floats, the Chinese American Community Center Folk Dance Troupe from Hockessin, Del., and the Isiserettes Drill & Drum Corps from Des Moines, Iowa.

Obama addressed cheering crowds at the Commander in Chief Ball, speaking by video to thank a group of troops in southern Afghanistan. Then he introduced his “date,” Michelle Obama, who danced with her husband in a ruby chiffon and velvet gown while Jennifer Hudson sang “Let’s Stay Together.”

Obama hinted only barely at issues likely to spark opposition from Republicans. His speech was less a list of legislative proposals than a plea for tackling challenges.

“We must act, knowing that our work will be imperfect,” he said, and today’s “victories will only be partial.”