WASHINGTON - Republican-appointed justices split with their Democratic colleagues in a dozen cases as an unprecedented dynamic shaped the Supreme Court term that ended last week.

The newest justices fueled the trend, rewarding the men who appointed them with predictable votes.

President Obama's choices, Sonia Sotomayor and Elena Kagan, voted in virtual lockstep and usually alongside fellow Democratic appointees Ruth Bader Ginsburg and Stephen Breyer. Former President George W. Bush's two selections, Chief Justice John Roberts and Justice Samuel Alito, voted together more than any other duo.

All told, Roberts and Alito voted together in 96 percent of cases in which both took part, according to Scotusblog, a website that tracks the court. Kagan and Sotomayor were the second-most cohesive pair, with 94 percent agreement.

"We're in a different era," said A.E. Dick Howard, a constitutional law professor at the University of Virginia in Charlottesville. "This is the way the Roberts court is going to be, especially now that we've seen enough of Sotomayor and Kagan to see that they agree with each other and the two of them in turn agree with Breyer and Ginsburg."

The high court closed its term with rulings striking down a California ban on the sale of violent video games to minors and part of Arizona's public-financing system for candidates seeking state office. The court will reconvene in October for a term that could include clashes over Obama's health-care law and same-sex marriage.

The court has long had its ideological divisions, sometimes so intense that feuding justices barely spoke to each other. Until now, those splits have always crossed party lines. Republican-appointed retired Justices John Paul Stevens and David Souter regularly voted with the court's liberal wing on social issues including the death penalty and abortion.

With Kagan and Sotomayor now occupying those two seats, the split can be a party-based one as well. The court's five Republican-appointed justices disagreed with their Demo-cratic-nominated colleagues in 10 cases this term, according to statistics compiled by Scotusblog.

In the cases that "most of us care about," the politics of the nine justices now align with those of the presidents who appointed them, says Barbara Perry, a presidential and Supreme Court scholar at the University of Virginia's Miller Center of Public Affairs. She called the phenomenon "unprecedented."

Business cases proved especially divisive. The justices split 5-4 in letting companies force their customers and employees to take disputes to arbitration without the option of class actions. The court also voted 5-4 to shield generic-drug makers from patient suits and to limit the ability of shareholders in mutual fund companies to press securities fraud suits.

The vote was 5-3 to uphold an Arizona law that threatens companies with the revocation of their corporate charters if they hire illegal immigrants. Kagan didn't take part because she played a role in the litigation as Obama's solicitor general.

In each case, the five Republican appointees - Roberts, Alito and Justices Antonin Scalia, Anthony Kennedy and Clarence Thomas - formed the majority.