Invading someone without losing all my troops?

So, yesterday I made a post about rushing a moderate AI, I have been practicing a lot and today I was at a point where I was at 13k score vs AI who was at 12k score, I decided to attack the AI because they were focusing on my ally (now down to 7k score or so) and I didn't want to get 2v1'd later in the game.

Here's what happened:

I used all my elite teutonic knights coupled with some hand cannons and some trebuchets, and by the time I arrived at my opponent's base with 70 soldiers, my opponent completely countered me with like 50-60 airblasters (archers?) and then counter-attacked me with a bunch of them + some infantry and some siege weapons..

it sucked because I had a higher score, but I instantly fell sub 12k because of that and I knew I had lost the game after he overrun my gates with 50+ soldiers after trying to defend.

So, what went wrong? was I supposed to wait until I had a way greater score? make more archers? what exactly? how do I attack without losing the game?