There may well have been a door that was closed, but it's impossible to answer.
On the other hand, it doesn't really matter. What kind of framework is behind it? We assume a regular stud frame?
In that case, just
1) Find out if there are any pipe or electrical installations in the wall.
2) Find three studs where you want the opening and
3) Go at it with a drill, crowbar, and reciprocating saw.
If you have stud A, B, and C, let's say, you cut the stud and use a horizontal stud (D) between A and C, then add two more studs to support D and form the width of the opening.