Just one small point to clarify, the UK was at war with Germany BEFORE USSR.
http://en.wikipedia.org/wiki/Military_history_of_the_United_Kingdom_during_World_War_II
Germany declared war on the US in 1941:
http://en.wikipedia.org/wiki/German_declaration_of_war_against_the_United_States_(1941)
Stalingrad:
http://en.wikipedia.org/wiki/Battle_of_Stalingrad
Don’t get me started on the lend lease in regards to the UK and US directed to the USSR.