I'm writing a term paper for history, and I wondering which is correct:

The 1920s was a period of...
The 1920s were a period of...

The first one sounds correct to me, but I want to be sure that the subject and verb agreed.

According to all the information I have (and looked for) it should be:
The 1920s were a period of...

However, the rest of the sentence may change that.
Can you send me the rest of it?

The 1920s was a period of discrimination, hostility, and intolerance towards minority groups in America.

When you're not sure, it's safer to change the wording. For instance -- you could say --
The decade of the 1920s was a period of . . .

My instinct is to consider the 1920s as singular since you're talking about one unit of time.

The 20's WAS a period. Period is singular so then the verb has to be singular. Period and 20's are one thing.