Vice President Pence said on a visit to South Korea on Monday that the U.S. "era of strategic patience is over" regarding North Korea and its nuclear and ballistic missile program."Since 1992, the United States and our allies have stood together for a denuclearized Korean Peninsula," Pence said at a joint news conference with acting South Korean President Hwang Kyo-Ahn in Seoul. "We hope to achieve this objective through peaceable means. But all options are on the table."Pence, whose father is a Korean War veteran, earlier visited the Demilitarized Zone between the Koreas, where he could see North Korean soldiers across the divide.Amid rising tensions with North Korea, Pence pointed to recent high-profile U.S. military actions in Syria and Afghanistan as evidence of the Trump administration's "strength and resolve.""North Korea would do well not to test his resolve — or the strength of the armed forces of the United States in this region," the vice president warned.Pence vowed "unwavering support" for South Korea, adding, "We are with you 100 percent."Just ahead of Pence's arrival in Seoul, North Korea attempted and failed to launch an unidentified missile in its latest weapons test, further raising international concerns. The day before, it "brandished what appeared to be long-range and submarine-based missiles as part of a military parade, celebrating the 105th birthday of its late founder, Kim Il Sung," as we reported.The U.S. moved a Navy strike group toward the Korean Peninsula earlier this month, which elicited threats from Pyongyang of "tough counteraction" should the U.S. attack, as The Two-Way reported.So why the recent escalation of tensions with North Korea? Joel Wit, senior fellow at the U.S.-Korea Institute at the Johns Hopkins School of Advanced International Studies, explains on Morning Edition: