In the dark
Your game is unfortunately very shallow and lackluster.
It has the makings of a very great game, but ends up being hollow. There's nothing for the gamer to do but mash the number keys during the battle (and the occasional mouse click).
Further, the game doesn't have you "enter enemy territory by air, sea and land". It's air, sea OR land. It's like playing three parallel games at once. Why not find a way to link them together in later stages? (And how about branching the levels so that the game is less linear?)
What's more, you don't give the gamer any stats to judge their units by. How am I supposed to know how to spend my money? And in the battle, how am I supposed to know how much my units cost? You should post it for us. You took the time to make a useless options menu, but no help button.
And again, in battle there is almost nothing to do! Why not let us command our troop movement? And maybe give us a heads up as to the enemy's production so that we can actually have some sort of strategy once the battle begins.
Finally, make some difficulty levels. This game is way too easy.
I really hope you make a sequel, because I think this game has a lot of potential!