WASHINGTON — 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 a second inaugural address that broke new ground by assigning gay rights a prominent place in the wider struggle for equality for all.

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 from specially constructed flag-bedecked stands outside the Capitol after reciting the oath of office that all presidents have uttered since the nation’s founding.

The events highlighted a day replete with all the fanfare that a security-minded capital could muster — from white-gloved Marine trumpeters who heralded the arrival of dignitaries on the inaugural stands to the mid-winter orange flowers that graced the tables at a traditional lunch with lawmakers inside the Capitol.

The weather was relatively warm, in the mid-40s, and while the crowd was not as large as on Inauguration Day four years ago, it was estimated at up to 1 million.

Big enough that he turned around as he was leaving the inaugural stands to savor the view one final time.

“I’m not going to see this again,” said the man whose political career has been meteoric — from the Illinois Legislature to the U.S. Senate and the White House before marking his 48th birthday.

On a day of renewal for democracy, everyone seemed to have an opinion, and many seemed eager to share it.

“I’m just thankful that we’ve got another four years of democracy that everyone can grow in,” said Wilbur Cole, 52, a postman from suburban Memphis, Tenn., who spent part of the day visiting the civil rights museum there at the site where the Rev. Martin Luther King Jr. was assassinated in 1968.

The inauguration this year shared the day with 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 been Abraham Lincoln’s. The president also paused inside the Capitol Rotunda to gaze at a dark bronze statue of King.

Others watching at a distance were less upbeat than Cole. Frank Pinto, 62, and an unemployed construction contractor, took in the inaugural events on television at a bar in Hartford, Conn. He said because of the president’s policies, “My grandkids will be in debt and their kids will be in debt.”

The tone was less overtly political in the nation’s capital, where bipartisanship was on the menu in the speechmaking and at the congressional lunch.

“Congratulations and Godspeed,” House Speaker John Boehner, a Republican, said to Obama and Vice President Joe Biden as he presented them with flags that had flown atop the Capitol.

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.

The crowds were several rows deep along parts of the route, and security was intense. More than a dozen vehicles flanked the president’s limousine as it rolled down Pennsylvania Avenue, and several agents walked alongside on foot.

As recent predecessors have, the president emerged from his car and walked several blocks on foot. His wife, Michelle, was with him, and the two held hands while acknowledging the cheers from well-wishers during two separate strolls along the route.