PMP Certification Monitoring and Controlling Test 3

A project manager is leading a team with members from many different countries. As they began to work together, they were struggling to cooperate. This was accepted as the normal 'storming' phase of team development, but the team has not gotten past this phase and the project is beginning to fall behind schedule.
What conflict-resolution technique should be used to help the team progress to the 'norming' phase?