I recently played axis and allies 1941 for the first time with a friend and at one point during gameplay he took over my capital with a bomber by destroying my only tank and used its last movement to take it over later I was doubtful so I looked in the rulebook days later and confirmed that planes can never take over enemy territory I brought this to his attention and he agreed that he shouldn't have took it over but then argued that I would have lost my economy anyway because his plane destroyed my capital making it neutral territory until I took it back I don't think this is the case but just to be sure can planes or any unit destroy your economy in such fashion. To simplify my question can industry be destroyed.
An air unit cannot capture a territory; since the territory is not captured it would retain whatever control marker was on it. There are no rules to "destroy" a capital or industrial complex. A territory cannot become neutral; the only neutral territories are already defined on the board. http://axisallies.com/rules/axis-allies-rules-1941.pdf
I +1 the above answer, Only LAND units can take territory, NOT PLANES. In your situation.. when he took your tank out, thats all he did. There is no creating natural zone or destroying factories.
Just in case you didnt know, a player (allies or axis powers) wins when they take 2 capitals. and the game DOES NOT end until the end of the americans turn, so you have till then to do what you go to do!
I see this a-lot with people who dont know the rules to the game.. they make up their own rules and make it sound convincing. If it seems fishy, then its wrong.