Dublin, Ireland (CNN) -- Thousands of jubilant Irishmen and women gave U.S. President Barack Obama a virtual hero's welcome Monday, embracing him as one of their own in a visit that included a campaign-style speech in downtown Dublin and a stop at the president's ancestral home.
Addressing an estimated crowd of 25,000 people at Dublin's famed College Green, Obama praised the "centuries-old relationship" between Ireland and America, and said he had traveled to Ireland "to reaffirm those bonds of affection."
Despite the warm welcome, Obama departed Ireland a day earlier than planned and flew to England on Monday night instead of Tuesday to avoid any potential complications resulting from a plume of volcanic ash spreading from a volcano in Iceland.
The Ireland stop came on the first day of Obama's six-day, four-country European tour that also takes the president to France and Poland.
The state of the global economy and the tumult in the Arab world will be high on the president's agenda during his tour, according to White House Press Secretary Jay Carney.
Later in the week, Obama plans to attend the Group of Eight meeting in France, joining the leaders of Canada, France, Germany, Italy, Japan, Russia and the United Kingdom.
Obama's visit started, however, with a nod to domestic politics. His speech in Dublin on Monday repeatedly referenced the 19th-century flood of Irish immigration to the United States, and the contributions of the Irish to American life.
"Never has a nation so small inspired so much in another," Obama said. "Irish signatures are on our founding documents. Irish blood was spilled on our battlefields. Irish sweat built our great cities.
"You can say there has always been a little green behind the red, white, and blue," he declared.
Obama also sought to reassure the Irish that their country, deeply shaken by the growing international debt crisis, will work its way out of its current economic troubles.
"Your best days are still ahead," he said. "Remember whatever hardships winter may bring ... spring's just around the corner."
"Yes we can," he said -- a reference to his 2008 campaign slogan.
The president was introduced to the crowd in Dublin by Irish Prime Minister Enda Kenny.
Obama "doesn't just speak about the American dream. He is the American dream," Kenny declared.
During a meeting with Kenny earlier in the day, Obama praised Ireland for its work on issues of peace, security and human rights, and cited Ireland's contribution to an agreement that brought peace to Northern Ireland.
"Ireland punches above its weight," Obama said. "All of that makes a huge difference around the world.
"I wanted to just express to the Irish people ... how inspired we have been by the progress that has been made in Northern Ireland," he said. "It speaks to the possibilities of peace and people and long-standing struggles being able to reimagine their relationships."
Obama planted a tree -- an upright Irish oak -- in a park with trees planted by former Presidents John F. Kennedy and Bill Clinton.
The president also made time for a brief visit to the village of Moneygall, believed to be the birthplace of one of his great-great-great-grandfathers.
Obama was greeted by there by cheering crowds lining the streets despite occasional rain showers. He also briefly ducked into a pub to sip a Guinness beer.
"It tastes so much better here than it does in the States," Obama joked. "You're keeping all the best stuff here."
"I just want you to know the president pays his bar tab," he said.
"For me to make such a personal connection like this ... is spectacular," he said.
Situated in central Ireland between Dublin and Limerick, Moneygall underwent a patriotic facelift in preparation for the presidential visit. American flags were hung in front of homes and stores.
Genealogists at Ancestry.com first shed light on Obama's Irish roots when he was campaigning for the presidency. They traced his Irish ancestry several generations back to Fulmoth Kearney, the president's great-great-great-grandfather on his mother's side, who immigrated from Moneygall to Ohio in 1850.
Maybe it was that "luck o' the Irish" -- or perhaps support from some of the 40 million Irish-Americans -- that helped Obama win the presidential nomination.
"It never hurts to be a little Irish when you're running for the presidency of the United States of America," Obama joked during a campaign stop in 2008.
CNN's Alan Silverleib, Shawna Shepherd and Brianna Keilar contributed to this report