We are ready to invade enemy territory.

We are conducting training to devise strategies against hypothetical enemies.

The enemy general is approaching our camp.

Enemy troops are approaching our position.

He experienced his first encounter with the enemy on the battlefield.

He encountered the enemy on the battlefield.

The signal from the cell phone relay-station in this area is weak.

He admitted that it is difficult to execute the plan, saying 'it is easier said than done.'

Well then, I'm off.

He said, 'It's difficult to make a life,' explaining the phrase 'When a man steps over the threshold, he has seven enemies.'