I dont think you are fighting above london. Thats why you dont see buildings and why you´re allowed to use Poison and bombs against the germans. I think you are flying in the south-east of London because this is (after the nuking of paris, which makes this way dangerous) the way, which the germans would take. Why the AA-Guns are firing at you? German parachuters have landed and build up something which prevents the royal Airforce from escaping.
Ok, little Walktrough :
1. Desolation Peak: Use 1 green smoke plant at first and UPGRADE! The only advancement, that the enemy have, is his big range, but fully upgraded your bots are more effective. Keep building smoke plants and dont forget upgrades, and you will win.
2.Vulcano Island: Use your new pyramids to encounter this fast moving bots. The enemy do not have anything with a big enough range to counter the mummy bots. A very easy stage.
3. Sun Valley Hills: A little bit difficult. I would say, that mummys will bring the win to you, but the spiderbots are hard. Upgrade is important. Try to outnumber the enemy with mass Mummys. A hospital will be very useful.
4. Twilight field: Sounds harder then it is. Outnumber the tanks with mummys and revive fallen mummys with medics. Upgrade upgrade upgrade!
5. Judgement City: Start with Spiderbots and later build a tank factory. That will hold off he enemy as long as you want.
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against the sword wielding enemys: use gunners in hunge number and research personal shields.
A bigger challenge were the aerial drogs, but if you upgrade everything you can (except freeze bullets, i havent tried it yet), you can shoot them down.
theres a little Mistake (maybe only German?):
I´ve won my first battle, 2 enemy units killed. but they do not appear at "Einheiten vernichtet" (units destroyed). They appear at "Einheiten verloren"(Units lost)