I'm not denying that things may have been different had France attacked Germany across the Maginot Line, but they didn't because they weren't ready. Also, Britain wasn't in a position to invade Germany even if they wanted to; however, they started attacking German shipping and industry from the air within the first week of September '39 so they were fulfilling what of their promise they could.
Of course the Americans didn't promise anything - why would they? The point is, its not exactly fair to call France and Britain "lazy cowards" because they didn't assult Germany immediately. They (and most of the world I would state) believed they had more time to prepare. Germany overran Poland in 20 days or so didn't they? If they really knew that was possible (which I don't believe they did) then shame on them for not being more prepared, but I think since England wasn't mobilized, and France was busy trying not to fall apart politically, they did what they could manage. Obviously it wasn't near enough, and they let the Polish down. Are they "lazy cowards" for that? No way.