Question regarding bankruptcies and MERRILL

Hi, I am not really familiar in this field so i hope you guys could help. I was tasked to make a term paper of some sort regarding the causes on how MERRILL got broke or something like that. My questions are:

How do big banks such as Merrill get into a possibility of being bankrupt or how do banks go bankrupt in general?

What were the causes of MERRILL going into bankruptcy?

and...

Bank of America bought Merrill... so why Merrill and not Lehman Brothers or the other banks? What does Merrill have that none of the other banks have or something like that?

If possible, could you provide me with a link so i can fully understand this better? I'm not living the US so my knowledge about these things are low... Hope you could help. Thanks.

i cant even attempt to answer this in less than 100,000 words

-bit off more than they could chew. no risk mgmt. over leveraged against toxic assets

-merrill has the largest brokerage force in the world...17k brokers. combine that with BAC's enormous depositor base and you have a lot of synergy (fees)