Why do Muslims join kuffar armies?

Queen should first determine how many gods she believes in, 3 gods or 1 god.If one god then his name and if his name is not jesus(p.b.u.h)and holy ghost then what position and status do jesus(p.b.u.h) and holy ghost hold in christianity.
this is most vague and unclear oath i have ever seen.it actually questions foundation of christianity.