Per Wikipedia:

"If Bell chooses to stay loyal to Perseus they will trick the team into a trap and kill them with the help of Perseus and the Soviet Army before they activate the nukes. If Bell refuses to kill the team, Bell is Executed by Adler but the nukes will still go off. Europe is devastated by the explosions and public opinion of the United States plummets. The CIA is forced to erase the existence of Adler and his team in an effort to cover up the United States' involvement in Operation Greenlight. Perseus boasts that his agents in Europe will take advantage of the chaos to infiltrate every European government and turn them towards the Soviet Union, while his agents in the United States will continue to undermine the country. "