Final answer:
The number of political parties in a democratic legislature is primarily influenced by the country's electoral system, with proportional representation leading to multi-party systems and plurality voting systems often resulting in two-party systems.
Step-by-step explanation:
The number of political parties in a democratic legislature will most likely be influenced by the country's electoral system. Presidential regimes with plurality voting and single-member districts, such as the one in the United States, often encourage a two-party system. In contrast, parliamentary systems with proportional representation allow for more viable third parties and typically result in a multi-party system. For example, coalition governments are common in countries with competitive multi-party systems, and they form when no single party gains a majority, leading parties to join together to create a majority in the legislature. The type of electoral system essentially dictates the number of competitive parties within the political system and influences legislative dynamics significantly.