What are the invalidators of the marriage contract?

Question:
He says in the end of his questions: What are the invalidators of marriage in the Shari'ah, O honorable Shaykh?

Answer:
The invalidators are of different types: It may become clear that she is his sister through breastfeeding, in which case the marriage is invalid. It may become clear that she is his daughter through breastfeeding, in which case the marriage is invalid. It may become clear that she is his aunt through breastfeeding, in which case the marriage is invalid. It may become clear that she is his maternal aunt, in which case the marriage is invalid. It may become clear that the contract is not valid, and that he married her without a guardian, or without an offer and acceptance; in which case the marriage they claimed to be a marriage is invalid. It may be invalid because he married her during the waiting period before she completed the waiting period.
It may become clear that she has a husband who did not divorce her, in which case the marriage is invalid; because he married her while she was already married. The marriage may be invalid because he married her during the waiting period; her husband died and he married her before she completed the waiting period, in which case the marriage is invalid. Its invalidators are many, and the scholars have explained them. Yes.

The presenter: May Allah reward you with good, O honorable Shaykh Abdul Aziz.