In 1980s, M&A business of investment banks began a new stage in full swing. In addition to the United States, M&A business of investment banks has gradually developed in Western Europe and other countries and regions with developed market economy. The M&A business of investment banks is increasing, and the operating profit is also increasing. Various professional methods and skills of M&A and anti-M&A have been developed. Leveraged buyout (LBO), management buyout (MBO), junk bonds, bridge financing and other new technologies and tools that greatly promote the development of enterprise mergers and acquisitions, as well as famous anti-merger strategies such as poison pill, scorched earth and parkman, all came into being or matured at this stage. Since the mid-1980s, various powerful investment banks in the United States have followed the practice of investment groups and started the equity investment business of "acquiring enterprises-restructuring and selling". For example, Merrill Lynch followed KKR Group's approach to enter the leveraged buyout market, Faustmann Little Company of Lehman Brothers Group acquired Dokdo Pepper Company, and First Boston Bank acquired BTR (Complex Enterprise Group) and Dunlop Tire of Britain (Dunlop Tire Company). Throughout the 1980s, M&A business of investment banks developed rapidly in both depth and breadth, showing a diversified pattern. Investment banks not only serve people who buy enterprises, but also serve people who sell enterprises, and also provide anti-takeover services for target enterprises and their major shareholders; Not only provide consulting for customers, but also provide financing for customers; Not only do M&A planning and financial consultation for customers, but also directly buy and sell property rights (enterprises) as buyers or sellers; We should not only carry out mergers and acquisitions of listed companies, but also private companies ~