Explain this line in Kurt Vonnegut’s “Slaughterhouse Five” Please?

Question

“We were formed in ranks, with Russian soldiers guarding us-Englishmen, Americans, Dutchmen, Belgians, Frenchmen, Canadians, South Africans, New Zealanders, Australians, thousands of us about to stop being prisoners of war. And on the other side of the field were thousands of Russians and Poles and Yugoslavians and so on guarded by American soldiers.”

Why are the Russians and Americans on opposite sides here? Russia and America fought together in WW2.

Answer 1

They were fighting on the same side, but not "together"- they were in different areas. At some point, they met. The idea here is that each side is guarding allied personnel held as prisoners of war by the Germans in preparation for their release.

Answer 2

True, but we each had our own sectors.  The British and French had theirs too.

GOOGLE "allied sectors, Germany"...for maps.

I lived and worked in Germany for 9 years.

Answer 3

not at the beginning, at first Russia was fighting with the axis powers, till Hitler turned on them and started attacking them as well