[译] 我们必须防御敌人的入侵。
[误] We must defend the enemy’s aggression.

[正] We must defend ourselves against the enemy’s aggression.
[注] defend 的意思是 guard, make safe, 所以其宾语应该是保护的对象。表示“保护某人或某事物不受……”，应该说 defend sb./sth. against/from...