SPOILER : Easiest way to win story mode :

This is the easiest way that I found to clear story mode.

Warning

Don't read this guide if you want to figure how to beat story mode yourself.

Also this is made before the devs made a difficulty fix update.

How to :

As you can observe, I did a full line of archer (I placed a normal soldier for protection but really you don't need him).



Just upgrade their attack speed and attacks and you're good.

Conclusion

Took me a while before figuring that one out.

Also this will probably be useless after the difficulty update...

[Normandy Beach]

I had somebody ask me for the last challenge, unfortunately I did finish it when it came out and I don't remember how I did it but yeah I can assure you there's probably only 2 or 3 ways to complete it.

[D.G.A.]

I already finished the story mode but thanks for that.
The only thing that I was NEVER able to finish was the last challenge where there are enemies coming from 4 different directions.
That is just ridiculous to me and feels more like bad gameplay design than anything else.