A conglomerate is the combination of two or more corporations engaged in entirely different businesses that fall under one corporate group, usually involving a parent company and many subsidiaries. Often, a conglomerate is a multi-industry company. Conglomerates are often large and multinational.
Conglomerates were popular in the 1960s due to a combination of low interest rates and a repeating bear/bull market, which allowed the conglomerates to buy companies in leveraged buyouts, sometimes at temporarily deflated values. Famous examples from the 1960s include Ling-Temco-Vought,ITT Corporation,Litton Industries,Textron,Teledyne. Because of low interest on the loans, the overall return on investment of the conglomerate appeared to grow. Also, the conglomerate had a better ability to borrow in the money market, or capital market, than the smaller firm at their community bank.
For many years this was enough to make the company's stock price rise, as companies were often valued largely on their return on investment. The aggressive nature of the conglomerators themselves was enough to make many investors, who saw a "powerful" and seemingly unstoppable force in business, buy their stock. High stock prices allowed them to raise more loans, based on the value of their stock, and thereby buy even more companies. This led to a chain reaction, which allowed them to grow very rapidly.
However, all of this growth was somewhat illusory and when interest rates rose to offset inflation, conglomerate profits fell. Investors noticed that the companies inside the conglomerate were growing no faster than before they were purchased, whereas the rationale for buying a company was that "synergies" would provide efficiency. By the late 1960s they were shunned by the market, and a major sell-off of their shares ensued. To keep the companies going, many conglomerates were forced to shed the industries they had recently purchased, and by the mid-1970s most had been reduced to shells. The conglomerate fad was subsequently replaced by newer ideas like focusing on a company's core competency.