Here's why:
* Independent Clause: A group of words with a subject and verb that can stand alone as a complete thought.
* Compound Sentence: Two or more independent clauses joined together.
The conjunction acts as the "glue" that connects the two independent clauses and makes them a single, grammatically correct sentence.
Examples:
* The sun was shining, and the birds were singing. (conjunction: and)
* I went to the store, but I didn't buy anything. (conjunction: but)
* She studied hard, so she got a good grade. (conjunction: so)
Without a conjunction, you would have two separate sentences, not a compound sentence.
For example:
* The sun was shining. The birds were singing. (two separate sentences)