Why does a programming language need keywords?

Question

For example (in C):

int break = 1;
int for = 2;

Why will the compiler have any problems at all in deducing that break and fo

Answer 1

Since it's tagged C, the original C language was such that by default any variable was defined as type int.

It means that foo; would declare a variable of type int.

Let's say you do break;. So how does the compiler know whether you want to declare a variable named break or use the keyword break?