WASHINGTON — The United States capped its best year for hiring in 15 years with a healthy gain in December, and the unemployment rate reached a six-year low. The numbers support expectations that the United States will strengthen further this year even as overseas economies stumble.

The Labor Department said today that employers added 252,000 jobs last month and 50,000 more in October and November combined than it had previously estimated. The unemployment rate dropped to 5.6 percent from 5.8 percent in November. The rate is at its lowest point since 2008.

Yet wage growth remains weak. Average hourly pay slipped 5 cents in December. And the unemployment rate fell partly because many of the jobless gave up looking for work and so were no longer counted as unemployed.

American businesses have been largely shrugging off signs of economic weakness overseas and continuing to hire at healthy rates. The U.S. economy's steady improvement is especially striking compared with the weakness in much of the world.

WASHINGTON — California Democratic Sen. Barbara Boxer, a tenacious liberal whose election to the Senate in 1992 heralded a new era for women at the upper reaches of political power, announced Thursday she will not seek re-election to a new term next year.Boxer's retirement sets off a free-for-all among a new generation of California Democrats, who have had few offices to aspire to while Boxer and Sen. Dianne Feinstein had a lock on Senate seats.A staunch supporter of abortion rights, gun control and environmental protections, Boxer has said she is most proud of the vote that she cast against the war in Iraq.

TUCSON, Ariz. — Former Arizona Rep. Gabby Giffords spent part of the fourth year anniversary of the mass shooting that left her gravely wounded meeting with President Barack Obama as her city paused to remember the tragedy that left six dead and 13 injured.Nineteen bells rang Thursday morning to honor the victims of a shooting in Tucson at a political event hosted by Giffords. Giffords did not attend the event but met with Obama during his visit to Phoenix.“It was four years ago today that Gabby and some other wonderful Arizonans were gunned down outside a supermarket in Tucson. It's a tough day for a lot of folks down there. We keep them in our thoughts and prayers,” Obama said.