The United States and South Korea have begun 10 days of joint military exercises on Monday. But the exercises will have fewer troops, vehicles and other equipment than last year. Military leaders say these exercises, also known as war games, are needed to maintain operational readiness. But there are concerns that a show of force could again increase tensions in the region. The yearly US-South Korea war games are large military planning and coordination exercises. They are designed to respond to computer-simulated North Korean attacks. About 17,500 American troops will participate in this year’s exercises, along with 50,000 South Koreans. That is down from 25,000 American troops in 2016. Military leaders say these annual war games are needed to train new soldiers in the region.