U.S. Defense Secretary Robert Gates made an unannounced trip to Pakistan today. He's hoping to improve relations with the country. He also wants to encourage the government there to root out Taliban militants. This is Gates' first visit to Pakistan since U.S. President Barack Obama took office last year. He met with Pakistan's defense minister in Rawalpindi. Pakistan and the U.S. have been allies for years. But ties have been strained since the U.S. called on Pakistan to step up its efforts to stop militants from crossing the Afghan border.