WASHINGTON (AP) — President Barack Obama vowed Thursday the United States will remain the world’s pre-eminent military power even as the Pentagon scales back spending, shrinks the Army and Marine Corps, and pulls back from Europe.In a rare appearance at the Pentagon, Obama said the U.S. is “turning a page” after having killed al-Qaida leader Osama bin Laden, withdrawn troops from Iraq and begun to wind down the war in Afghanistan. He outlined a vision for the future that would ensure an uncompromised U.S. military strength operating with less money.“Our military will be leaner, but the world must know the United States is going to maintain our military superiority,” Obama said, with Defense Secretary Leon Panetta and the Joint Chiefs of Staff chairman Gen. Martin Dempsey at his side.Obama said his administration would not repeat the mistakes made after World War II and Vietnam when defense reductions left the military ill-prepared.“As commander in chief, I will not let that happen again,” he said. “Not on my watch.”Both Panetta and Dempsey said they anticipate heavy criticism of their new strategy, which is meant to guide future defense budgets, including the 2013 spending plan that Obama will submit to Congress in February.The criticism from Republicans came quickly.Rep. Howard “Buck” McKeon, R-Calif., chairman of the House Armed Services, issued a statement saying, “This is a lead-from-behind strategy for a left-behind America.”