SEOUL, South Korea (AP) — Tens of thousands of North Koreans marched in anti-U.S. rallies over the weekend, pledging “merciless” revenge against “U.S. imperialists,” as the country marked the 73rd anniversary of the start of the Korean War, state media said Monday. Photos sent by Park Sang-hak showed a placard with a picture of North Korean leader Kim Jong Un and a message that highlighted how his grandfather, Kim Il Sung, was responsible for starting the Korean War. North Korea is extremely sensitive about any outside attempt to undermine Kim’s leadership and weaken his absolute control over the country’s 26 million people. They vowed tighter diplomatic and security cooperation between Washington, Seoul and Tokyo to cope with the threat, the South Korean ministry said.