For example lets say we start colonies on Mars, and they rebel, and we have to send a military force there.

Not as we know science now.

The critical factor is time- both communications and transit. The closest real-world parallel was the 18th Century British Empire. The Royal Navy was the most powerful military force on Earth, and they were still incapable of suppressing the American Revolution. (I know it was His Majesty's Army on the ground, but they couldn't have gotten to the sharp end without the Navy.) By the time London (A) found out things had popped at Lexington and Concord, (B) geared up to reinforce Burgoyne & Co., and (C) gotten there with Cornwallis & Co., the Colonials had (A) made too many gains, (B) had attracted too much support (notably from France), and (C) were too well organized with too much defense in depth for any practical countermeasures to work. The success of the Revolution was not a foregone conclusion, but the Empire had several strikes against it right from the beginning. (And yes, Washington, Franklin, Jefferson & Co. knew all this, else they wouldn't have tried it- they were military men themselves, after all.) Any "colonial revolt" in a hypothetical "Solar Empire" would be operating under similar constraints on the central power, i.e. Earth. For good examples of how badly things could go for Earth under such circumstances, I'd suggest you read "The Moon Is A Harsh Mistress" by Robert Heinlein, or (at short interstellar range) "Revolt on Alpha C" by Robert Silverberg. (There are probably others that address the same issues, but these are two I've read and found interesting.)

That is a pretty good post eon for such a far fetched subject. I think I will read those books.

The Heinlein book is back in print (three cheers for our side!) The Silverberg book, which as far as I have been able to ascertain may have been his first full-length novel (actually novella; about 18,000 words)as opposed to short stories, was published as a juvenile by Scholastic Book Services in the 1960s. I don't know if it has been reprinted since, but it's possible. Good luck, and happy reading.