Yes, INVADE is a Scrabble word!

Letter values in Scrabble US: I 1, N 1, V 4, A 1, D 2, E 1.

Is it a valid word?

INVADE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

march aggressively into another's territory by military force for the purposes of conquest and occupation
to intrude upon, infringe, encroach on, violate
occupy in large numbers or live on a host
penetrate or assault, in a harmful or injurious way

Also: intrude on, obtrude upon, encroach upon.