Which is the most effective way to combine sentence 2 and 3? that ancient land was located in the middle east. the middle east is a hot and sunny part of the world.

I do not know if this is a multiple-choice question or not, but I would contend that the most effective way to combine these two sentences is by means of a relative clause.

Explanation: A relative clause simply gives more information about a person, an artifact or a situation by means of a relative pronoun. Sentence 3 gives additional information about the location where the land in sentence 2 was located (the Middle East). Since the Middle East can be considered a thing, we'll use the pronoun which followed by a comma and introduce the additional information: "The ancient land was located in the Middle East, which is a hot and sunny part of the world."