Banks in The Economy.....

The economic functions of banks include:

1.     Issue of money, in the form of banknotes and current accounts subject to cheque or payment at the customer's order. These claims on banks can act as money because they are negotiable or repayable on demand, and hence valued at par. They are effectively transferable by mere delivery, in the case of banknotes, or by drawing a cheque that the payee may bank or cash.
2.   Netting and settlement of payments – banks act as both collection and paying agents for customers, participating in interbank clearing and settlement systems to collect, present, be presented with, and pay payment instruments. This enables banks to economize on reserves held for settlement of payments, since inward and outward payments offset each other. It also enables the offsetting of payment flows between geographical areas, reducing the cost of settlement between them. 
3.  Credit intermediation – banks borrow and lend back-to-back on their own account as middle men. 
4. Credit quality improvement – banks lend money to ordinary commercial and personal borrowers (ordinary credit quality), but are high quality borrowers. The improvement comes from diversification of the bank's assets and capital which provides a buffer to absorb losses without defaulting on its obligations. However, banknotes and deposits are generally unsecured; if the bank gets into difficulty and pledges assets as security, to raise the funding it needs to continue to operate, this puts the note holders and depositors in an economically subordinated position. 
5.  Asset liability mismatch/Maturity transformation – banks borrow more on demand debt and short term debt, but provide more long term loans. In other words, they borrow short and lend long. With a stronger credit quality than most other borrowers, banks can do this by aggregating issues (e.g. accepting deposits and issuing banknotes) and redemptions (e.g. withdrawals and redemption of banknotes), maintaining reserves of cash, investing in marketable securities that can be readily converted to cash if needed, and raising replacement funding as needed from various sources (e.g. wholesale cash markets and securities markets). 
6. Money creation/destruction – whenever a bank gives out a loan in a fractional-reserve banking system, a new sum of money is created and conversely, whenever the principal on that loan is repaid money is destroyed.
   

Bank crisis

Banks are susceptible to many forms of risk which have triggered occasional systemic crises. These include liquidity risk (where many depositors may request withdrawals in excess of available funds), credit risk (the chance that those who owe money to the bank will not repay it), and interest rate risk (the possibility that the bank will become unprofitable, if rising interest rates force it to pay relatively more on its deposits than it receives on its loans).

Banking crises have developed many times throughout history when one or more risks have emerged for a banking sector as a whole. Prominent examples include the bank run that occurred during the Great Depression, the U.S. Savings and Loan crisis in the 1980s and early 1990s, the Japanese banking crisis during the 1990s, and the sub-prime mortgage crisis in the 2000s.
 

Size of global banking industry

Assets of the largest 1,000 banks in the world grew by 6.8% in the 2008/2009 financial year to a record US$96.4 trillion while profits declined by 85% to US$115 billion. Growth in assets in adverse market conditions was largely a result of recapitalization. EU banks held the largest share of the total, 56% in 2008/2009, down from 61% in the previous year. Asian banks' share increased from 12% to 14% during the year, while the share of US banks increased from 11% to 13%. Fee revenue generated by global investment banking totalled US$66.3 billion in 2009, up 12% on the previous year.

The United States has the most banks in the world in terms of institutions (5,330 as of 2015) and possibly branches (81,607 as of 2015). This is an indicator of the geography and regulatory structure of the US, resulting in a large number of small to medium-sized institutions in its banking system. As of November 2009, China's top 4 banks have in excess of 67,000 branches (ICBC:18000+, BOC:12000+, CCB:13000+, ABC:24000+) with an additional 140 smaller banks with an undetermined number of branches. Japan had 129 banks and 12,000 branches. In 2004, Germany, France, and Italy each had more than 30,000 branches – more than double the 15,000 branches in the UK.
 

Mergers and acquisitions
 

Between 1985 and 2018 banks engaged in around 28,798 mergers or acquisitions, either as the acquirer or the target company. The overall known value of these deals cumulates to around 5,169 bil. USD. In terms of value, there have been two major waves (1999 and 2007) which both peaked at around 460 bil. USD followed by a steep decline (-82% from 2007 until 2018).