Question

Is the sentence a simple, compound, or complex? After some time passed, baseball's second league was created?

Answer 1

Answer:

The sentence above is a complex sentence.

Explanation:

A complex sentence has one independent clause and at least one dependent clause. An independent clause can stand alone as a sentence as it represents a complete thought. In the sentence above, the dependent clause is the following prepositional phrase: "after some time passed". Then the independent clause is the following sentence: "baseball's second league was created".  As you can see, 1 cannot stand on its own because it does not represent a complete idea.

1) *After some time passed

2) Baseball's second league was created

Answer 2

This sentence is complex.
The dependent clause is After some time passed, and the independent one is the rest of the sentence. 
A simple sentence would have only one independent clause, and a compound sentence would have at least two independent clauses.