Tracing back to history, merger and acquisitions have evolved in five stages and each of these are discussed here. As seen from past experience mergers and acquisitions are triggered by economic factors. The macroeconomic environment, which includes the growth in GDP, interest rates and monetary policies play a key role in designing the process of mergers or acquisitions between companies or organizations.
First Wave Mergers
The first wave mergers commenced from 1897 to 1904. During this phase merger occurred between companies, which enjoyed monopoly over their lines of production like railroads, electricity etc. the first wave mergers that occurred during the aforesaid time period were mostly horizontal mergers that took place between heavy manufacturing industries.
End Of 1st Wave Merger
Majority of the mergers that were conceived during the 1st phase ended in failure since they could not achieve the desired efficiency. The failure was fuelled by the slowdown of the economy in 1903 followed by the stock market crash of 1904. The legal framework was not supportive either. The Supreme Court passed the mandate that the anticompetitive mergers could be halted using the Sherman Act.
Second Wave Mergers
The second wave mergers that took place from 1916 to 1929 focused on the mergers between oligopolies, rather than monopolies as in the previous phase. The economic boom that followed the post world war I gave rise to these mergers. Technological developments like the development of railroads and transportation by motor vehicles provided the necessary infrastructure for such mergers or acquisitions to take place. The government policy encouraged firms to work in unison. This policy was implemented in the 1920s.

The 2nd wave mergers that took place were mainly horizontal or conglomerate in nature. Te industries that went for merger during this phase were producers of primary metals, food products, petroleum products, transportation equipments and chemicals. The investments banks played a pivotal role in facilitating the mergers and acquisitions.
End Of 2nd Wave Mergers
The 2nd wave mergers ended with the stock market crash in 1929 and the great depression. The tax relief that was provided inspired mergers in the 1940s.
Third Wave Mergers
The mergers that took place during this period (1965-69) were mainly conglomerate mergers. Mergers were inspired by high stock prices, interest rates and strict enforcement of antitrust laws. The bidder firms in the 3rd wave merger were smaller than the Target Firm. Mergers were financed from equities; the investment banks no longer played an important role.