The correct answer is option 'D', the Second International.

The Second International was a major international organization that represented socialist and labor parties from around the world. It was founded in 1889 and existed until 1916. The Second International played a significant role in the development of socialist and labor movements, as well as in the promotion of workers' rights and social justice.

Formation and Purpose:
The Second International was formed with the aim of promoting international cooperation among socialist and labor parties. Its primary purpose was to unite socialist parties and trade unions across different countries to work towards achieving common goals, such as improving working conditions, advocating for workers' rights, and advancing the socialist cause.

Membership and Structure:
The Second International included various socialist and labor parties as its members. It had a hierarchical structure, with an executive bureau responsible for overseeing its activities. The member parties held regular congresses to discuss and coordinate their actions.

Key Activities and Initiatives:
1. Workers' Rights: The Second International played a crucial role in advocating for workers' rights, including the establishment of an eight-hour workday, better wages, and improved working conditions. It organized strikes, demonstrations, and other collective actions to support workers' demands.

2. International Solidarity: The Second International promoted international solidarity among socialist and labor movements. It supported workers' struggles across different countries and provided assistance to oppressed workers and their organizations.

3. Opposition to War: One of the significant initiatives of the Second International was its opposition to war. During the early 20th century, as tensions escalated and eventually led to World War I, the Second International called for international efforts to prevent war and resolve conflicts peacefully.

4. Exchange of Ideas and Strategies: The Second International provided a platform for socialist and labor parties to exchange ideas, strategies, and experiences. It facilitated discussions on socialist theory, political tactics, and organizational methods, contributing to the development of socialist movements worldwide.

Legacy:
Although the Second International disbanded during World War I due to disagreements among its member parties regarding their stance on the war, its legacy and impact on the socialist and labor movements are significant. It laid the foundation for future international socialist organizations, such as the Socialist International, which was formed in 1951.

In conclusion, the Second International was a critical international body that united socialist and labor parties worldwide. It aimed to promote workers' rights, international solidarity, and socialist ideals. Despite its dissolution, its efforts and initiatives continue to shape the socialist and labor movements to this day.

Second international was an international body formed in the 1870s. It was set up to coordinate the ideas of the socialists throughout europe.