What economic development is characterized by the consolidation of various businesses into a single corporation?

The correct answer is related to the concept of horizontal integration. This economic development occurs when a company consolidates with other businesses that are in the same industry and operate at the same stage of production. The goal of horizontal integration is often to increase market share, reduce competition, and achieve economies of scale. This strategy was particularly prominent during the late 19th and early 20th centuries, as seen in the way companies like Standard Oil expanded their control over the oil industry.

In contrast, a merger is a broader term that can refer to any combination of two or more companies, whether they're in the same industry or not. Vertical integration, on the other hand, involves a company taking control of different stages of the production process, from raw materials to final product distribution. Lastly, monopoly formation describes a situation where a single company gains dominant control over a market, potentially through various means—including both horizontal and vertical integration—but is not strictly synonymous with the act of consolidation itself. Therefore, horizontal integration is the most appropriate term to describe the specific type of consolidation of similar businesses into a single entity.