- Did Americans invade our country or something? What's happening?
- Americans invaded our country or something? What's happening?
I know the statement one is correct. Is statements like 2 allowed in causal spoken English?
In casual spoken English, you could say either one. #1 is a straightforward question while #2 is more of an expression of disbelief or confusion, and it would usually be repeating something observed (or said by someone else).
Consider this short play:
It's grammatically a statement. So how can it be a question? Simple:
Intonation overrides grammatical structure.
When you end the sentence with rising intonation, you turn it into a question. And when you write a sentence like this, you indicate the rising intonation by using a question mark
Making questions in this manner is markedly informal, however. You should avoid doing so in formal situations, including formal essays and on tests. But it's perfectly appropriate in conversations and in online chat, for example.