The U.S. Marine Corps has left Iraq. The U.S. Army will remain behind to wrap things up. This is another old custom, going back to World War II. During the first American offensive in the Pacific, the 1942 invasion of Guadalcanal, the marines led the way. But once the heavy fighting was over, the marines departed, and the army finished up.
During the 2003 invasion, some 40,000 marines participated, and there were over 80,000 marines in the region at the time. A marine and army division advanced on Baghdad, fighting their way through the Iraqi army. After 2003, the number of marines in Iraq shrank, usually no more than 25,000. But the marines were always there, and lost 522 dead and 5,049 wounded in the process. Most of the navy casualties in Iraq (26 dead, 320 wounded) were sailors serving in support of the marines. There are 203,000 active duty marines, about seven percent more than there were in 2003.