The North’s announcement underscored leader Kim Jong Un’s determination not to back down in the face of his rivals’ push to expand their military exercises.But some experts say Kim also used their drills as an excuse to modernize his nuclear arsenal and increase his leverage in future dealings with Washington and Seoul.The North’s military statement didn’t explicitly mention a reported launch Thursday of an intercontinental ballistic missile aimed at hitting the U.S. mainland, though its main newspaper published a photo of an ICBM-like weapon as one that was used during last week’s testing activities.On Saturday, the final day of the air force exercises, the United States flew two B-1B supersonic bombers over South Korea in a display of strength against North Korea, the aircraft’s first such flyover since December 2017.After their annual meeting Thursday in Washington, U.S. Defense Secretary Lloyd Austin and South Korean Defense Minister Lee Jong-Sup issued a joint statement strongly condemning the North’s recent launches and carrying Austin’s warning that any nuclear attacks against the United States or its allies and partners “is unacceptable and will result in the end of the Kim regime.” South Korea’s military has previously warned the North that using its nuclear weapons would put it on a “path of self-destruction.” Both defense chiefs also agreed on the need to enhance combined exercises and training events to strengthen readiness against North Korean nuclear and missile threats."