By Laura Smith-Spark
BBC News, Des Moines
It was a night hailed by many of those taking part as a turning point for Iowa - and the American people.
Despite the cold, people turned out in record numbers to participate in more than 1,700 caucuses across the state.
Iowa party members turned out in large numbers
And the candidates they backed - Barack Obama for the Democrats and Mike Huckabee for the Republicans - each talked of the result both as a "defining moment in history" and as a chance to reunite a divided America.
"This was a place where America remembered what it was to hope," said Barack Obama, speaking to jubilant supporters at a celebratory rally in Des Moines.
"This was a moment when we tore down barriers, when we finally gave Americans who had never participated in politics a reason to do so."
A few blocks away, Mr Huckabee, too, talked of a "new day" in American politics, one on which Iowa's voters had signalled their desire to see the country reunited.
"The people of Iowa made a choice and their choice was clear: it was choice for a change," he said.
Nonetheless, he cautioned supporters against assuming the battle was already won.
Obama now has "the big mo" - momentum - driving his campaign
"If this was a marathon, we've only run half of it - but we've run it well."
The next leg of the gruelling race will take the candidates to the small state of New Hampshire, which holds its primaries in just five days' time.
And it is there that the night's big losers - Hillary Clinton, who came in third behind John Edwards - and Mitt Romney, who failed to wrest Iowa from Mr Huckabee despite spending far more - will hope to recover their form.
But if Iowa's caucuses give their rivals a significant "bounce", they may have their work cut out despite their formidable campaign organisations in the state.
Key to the success of the Obama campaign, in particular, was the huge turnout of voters - some 239,000 for the Democrats, many of them attending caucuses for the first time.
Greenwood Elementary School in Des Moines, where Democrats caucused in the gym and their Republican counterparts in an upstairs classroom, was no exception.
In his first caucus, Michael Savala decided to support Barack Obama
Long lines formed as voters waited to register and, once inside, the crush made it hard for the Democrats - whose caucus rules require them to break up into groups supporting each candidate and be counted - to move around.
"It's a bigger group than we've ever had," said precinct chair Tom Fisher.
"I think the driving force is dissatisfaction with the current administration - and I think it means we are going to elect a Democrat in November."
It quickly became clear that the buzz surrounding the Obama supporters, many but not all of them young, was translating into numbers.
3 Jan: Iowa caucuses
8 Jan: New Hampshire primary
15 Jan: Michigan primary
19 Jan: Nevada caucuses; South Carolina primary (Rep)
26 Jan: South Carolina primary (Dem)
29 Jan: Florida primary
5 Feb: some 20 states including California, New York, New Jersey
The precinct's first count gave the Illinois senator almost half of the total 532 Democrats present - a significant increase on the 310 who turned out in 2004.
Among the first-time caucus-goers in Mr Obama's corner was Michael Savala, a 43-year-old lawyer.
"I've never done it before but I'm getting older and I appreciate the fact that we are the first in the nation, so I had better get down here and participate," he said.
"I wanted to support Mr Obama because he's young, he stands for change and I'm encouraged by a person of colour who is running for office. I'm in a minority myself and he's my candidate of choice."
Kelsey Mitchell, who will turn 18 in time to vote in November, said: "It was my first caucus and it was really crowded but it was exciting.
"I think everybody is ready for change and that's why they are here for Obama. It's a chance for Iowa to be about more than corn and soy beans."
Mike Huckabee appeals to these young voters
Two hours later at the party to celebrate Mr Obama's win, other supporters echoed their excitement.
"If he wins this election, it will be the biggest change in American history since the 1960s," said 18-year-old Chris Ajluni, from Johnston, Iowa.
Michael Lilly, 52, from Des Moines, said: "Personally, I think this is a huge turning point in American history, maybe in the history of the world, because it symbolises the first time in America in which race really isn't an issue.
"Barack has captured people's hearts and none of the other candidates have done that. It's something very few have achieved since JFK."
Mr Huckabee's supporters, celebrating his win a few blocks away, also spoke of his power to win the hearts of Republicans.
Many were evangelical Christians, drawn to the former Baptist preacher's socially conservative values - and his ability to connect with the concerns of ordinary folk.
"He brings a little bit of light and fun and he's always that way even when he's tired," said Des Moines resident Paula Maxheim. "We like where he stands on the issues - and people just like him."
Paula Maxheim is drawn to Mike Huckabee's conservative values
Steve Deace, a talk show host on local radio, agreed that it was Mr Huckabee's "chemistry" with the people of Iowa that had helped him to defeat Mr Romney, despite his deep campaign pockets.
Whether that recipe will work in New Hampshire, where evangelical Christians are far less numerous and Republicans tend to be more socially moderate, remains to be seen.
But one thing is clear: the race is far from over and all eyes will be watching, as America and the world seek clues to its future course.