The 2010 midterm elections caused a political quake in the United States, leading to the most significant seat changes in Congress in half a century.

The outcome of the elections -- a divided government where the presidency is controlled by one party and the Congress is controlled by the other -- would force President Barack Obama to change his way of proceeding with his policy agenda for the rest of his presidency.

Conservative resurgence

Riding a wave of voters' frustration with the sluggish economy and high unemployment, Republicans recaptured control of the House of Representatives, adding more than 60 seats, the biggest seat changes in the last 50 years. In the Senate, Republicans took over six seats from Democratic rivals with a narrowing margin of 47 to 53, even though they failed to claim majority in the chamber.

The outcome of the elections marked a comeback of the country's conservative power which has been largely dormant since 2006. Democrats won overwhelmingly in 2006 and 2008 midterm elections, ending up with significant advantages in both chambers that some political analysts believed were beyond their natural strength.

The elections last month resulted in not only fundamental change in the balance of power between the two parties, but also restructuring within each parties.

"An already polarized party system will become even more so; the new Republicans will be even more conservative, and the remaining Democrats will mostly be liberals," said William Galston, a political expert at the Brookings Institution.

Most of the Democrats who lost their races in this election year were moderate and conservative members, such as those of the Blue Dog Caucus, a group formed in 1995 to give conservative Democrats a unified voice in Congress. On the Republican side, a large number of newcomers in Congress either represent the conservative Tea Party views or be beholden to its supporters.

Exit polls also indicated conservatives are back outside the Capitol Hill. Nationally, the electorate was more conservative than in 2006 by nine percentage points and more so than in 2008 by seven points.

Cooperation or confrontation

In a divided Congress, both parties will find it difficult to push through big items of legislation, given the already polarized atmosphere in Washington. In the past two years, Republicans have been unified in voting against almost every Democratic initiative and was labelled "party of no" by critics.

"In the early months of next year, anyway, conservative enthusiasms will find vociferous expression, and confrontation will predominate," said Galston. "After that, the parties may find a way to cooperate on legislation -- but only if the American people insist on it. History suggests that the voters don't send people to Washington just to yell at each other for the next two years."

Republicans might well understand that voters are not going to buy a doing-nothing Congress. With part of the Congress in hand, they are also to take the blame for the country's troubles. Therefore, the strategy of saying no might have helped them win the election, it may not work in the next.

History shows that a divided government sometimes can be very productive. In 1994, Republicans chalked a historic victory in midterm elections by reclaiming control of both chambers. After an early period of intensive confrontation with then Democratic President Bill Clinton, Republican-led Congress was able to cooperate with the president and passed major legislations.

"But I'm skeptical that there will be significant cooperation after this election. One reason is the polarization. There isn't a lot of middle ground between the two parties," said John Fortier, a research fellow at the American Enterprise Institute.