The allies met at Tehran because it was considered a neutral location for all of the allies. It was also a good idea to meet here logistically due to Chinese and Egyptian involvement.
Great Britain, France, Soviet Union, and China were some of the main Allies. A good way to remember this is GFSUC.
the greatest amphibious operation in history
autobahn
Barbarossa
autobahn
This could be debatable depending on your perspective. Officially, Saudi Arabia and the United States are on good terms, and would probably be considered allies.
Officially the only allies that Australia has are; The United States of America and New Zealand, through the ANZUS Treaty. Other countries considered allies such as the United Kingdom have no official alliance, but will most likely aid Australia if it were to be invaded.
Immigrants, because they would vote for the people who provided jobs for them.
Not generally, if an accompanying priest considered that a particular tribe might be potential converts an alliance might be considered.
D day was considered the turning point in the war. where instead of the allies playing defense they invaded German controlled territory.
Only germany was considered a serious long term threat