Re: A friend asked this question about the Prophet...
With Khadija, it was a love marriage. I don't care what anyone says to contradict it. Khadija liked the Prophet, so she proposed. Simple. She was a widow, and she thought he'd make a good second husband.
Aisha - married her out of choice.
The rest of the ladies he married were all widows or divorced, and many of them were linked to various tribes - so they were strategic moves for a great part to get other tribes to convert and cooperate with him. Also, it was encouragement to marry widows, orphans, and divorcees - ladies who didn't get rishtaas that easily.