Simplify the following text for a Grade 11 native English-speaking person.
Original: The modern regiment 's size varies in number , scope and administrative role from country to country ( and might not exist in some military forces ) and sometimes even within the military of the same nations .
Simplified: The modern regiment 's size changes in number , purpose , and role from country to country ( and might not exist in some military forces ) and sometimes even within the military of the same nations .