Democratic Republic of the Congo
Central African Republic
and on the high seas in "Maritime Interception Operations"
Needless to say, only a few of these conflicts are well known to us. But President Obama, in the most recent report to Congress "consistent with the War Powers Resolution," says that U.S. forces equipped for combat have been deployed to these places. In addition, there may be secret operations run by the CIA and reported secretly to the congressional intelligence committees.
This is one of the few provisions of the 1973 war powers law that presidents have complied with -- notification of sending troops. But it's a useful reminder of the many hostile situations in which U.S. forces are deployed.