A key phrase in the second sentence is "the reason." This is like saying "because," in that it introduces a premise. The second sentence is a premise in support of the first sentence. Premises support conclusions, and not the other way around.
Conclusion: It is good to have national leaders voted out every few years. Why? Premise: Because reforms are generally undertaken early in a new government.
Note that the first sentence does not support any other part of the passage. This is the mark of a main conclusion, even if subsidiary conclusions are present.
Another clue here is the word "good." This is a matter of opinion, which is often the language of a conclusion. A statement that something is good, bad, should be done, or should not be done will usually indicate a conclusion.