I don't know how you program difficulty but after 30 years it gets ridiculously hard.

I get to year 34 and a freaking invincible army comes rolling out of nowhere!!

I managed to barely win just to be destroyed the next year by a same devastating attack.

Maybe tone it down so that you are not crushed 2 years in a row.

Awesome idea. it could use more units though.

So far this is the best way to increase typing speed.

However, there is a glitch, re-playing levels will unlock all episodes one by one. Playing the first level when the final level is unlocked will send me to the ending screen, for instance. Might wanna fix that.