The 6 mostly Muslim countries Trump tried to ban

Section 3 of the order blocks entry of people from Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen, for at least 90 days, regardless of whether or not they hold valid non-diplomatic visas. This order affects about 218 million people who are citizens of these countries.

Explanation:

The Department of Homeland Security (DHS) lists these countries as Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen.