The Cuban Missile Crisis was when USSR built missile bases in Cuba. This was a threat to the U.S. because the missiles could reach many major cities within the U.S. Due to this threat, the United States wanted the missiles removed.
During this period the USA and its friends in europe had lietraly 5 miles from the soviet union or Russian territory. at the time Russian did not have an short flight response in place to attack the usa. this ment we could lunch a nuclear strike at the Russians and Russia culd not responed against the usa for sevaral hours and the usa could likely mount a good defense and prevent an attack. so putting missiles in cuba seemed like it would "balance" the detrent.
