haha good one, i can't think of an explanation. the best i can do is this: if we were to arrange the sentence 'the world is against us' it makes sense 'the world is against we' doesn't make sense flip it back the original way 'it is us against the world' makes sense 'it is we against the world' does not make sense unless you change it a bit'. in which case it becomes, 'we are against the world' its the same rule with 'I/me' 'it is me against the world' is correct 'it is I against the world' is incorrect. however, if you change it, 'I am against the world' it makes sense.

Westlife??? If the song you mentioned were form the band, I love the band too :D The full sentence is: It's us against the world.

It is US who are against the world. It is WE who are against the world. I would say the second one is correct :D ^^ Nominative: We, Accusative: Us. the verb to be (of which "is" forms part) takes the nominative, not the accusative. "We" is the nominative pronoun. "Us" is the accusative pronoun.

It's not a sentence for a start. No verb! :) "(This is about) us against the world." "(It's a case of) us against the world."