California was the fastest growing state at this time, with the highest use of checking accounts (partially driven by many soldiers being paid via bank accounts during WWII) resulting in BofA being swamped by checks. By 1949 the branches had to close at 2:00pm in order to process the bookeeping by 5. To cope with the transaction volume, the bank invested heavily in information technology and is generally credited, together with GE and SRI, with inventing modern centralized bank operations in the form of ERMA, with a number of financial transaction processing technologies such as automatic check processing, account numbers, Magnetic Ink Character Recognition (MICR) and, based on these technologies, credit cards linked directly to individual bank accounts.
Because of the efficiency of these technologies, the bank had significantly lower administrative costs than other banks and was able to expand further, until it was the world's largest bank in the early 1970s.
After the consolidation of banks into the larger financial services industry, it is no longer the worlds leader (the worlds largest bank is Citigroup in terms of how much money they make, however in the simple terms of how much "money is in the bank" Deutche Bank would be the largest). If the pending merger with Fleet Boston goes through however, it will have the largest deposit market share in America however, with rougly 1 out of every 10 dollars in a bank, being in Bank of America).
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