Subsidiary Alliance System:
The Subsidiary Alliance System was a policy implemented by the British East India Company in India during the 18th and 19th centuries. Under this system, the Company entered into alliances with the princely states of India, wherein the states were required to accept British protection and the Company's control over their foreign affairs. In return, the Company promised to defend the states from external threats and rebellions. However, this system gradually led to the erosion of the sovereignty of the princely states and increased British influence and control in India.

Opium Wars:
The Opium Wars were a series of conflicts between China and Great Britain during the 19th century. These wars were primarily fought over the issue of the British opium trade in China. The British East India Company had been smuggling opium into China, which led to widespread addiction and economic decline in China. In response, the Chinese government attempted to suppress the opium trade, leading to conflicts with the British. The wars resulted in China's defeat and the signing of the Treaty of Nanking in 1842, which forced China to open its ports to British trade and cede Hong Kong to the British.

Black Hand:
The Black Hand was a secret nationalist society in Serbia during the early 20th century. It was formed with the aim of unifying all the territories populated by South Slavs into a single independent state. The Black Hand is most famously known for its involvement in the assassination of Archduke Franz Ferdinand of Austria in 1914, which triggered the outbreak of World War I. The assassination was carried out by a member of the Black Hand, Gavrilo Princip, and it led to a series of events that eventually led to the global conflict.

Frankfurt Parliament:
The Frankfurt Parliament, also known as the Frankfurt National Assembly, was a short-lived legislative body in Germany in 1848. It was convened in the city of Frankfurt with the aim of creating a unified and constitutional German state. The parliament consisted of elected representatives from various German states and territories. However, it faced several challenges, including disagreements over the form of government and the inclusion of Austria. Ultimately, the Frankfurt Parliament failed to achieve its goals, and its efforts were suppressed by conservative forces.

Militarism:
Militarism refers to the belief or policy of maintaining a strong military force and using it aggressively to pursue national interests. It is often associated with the prioritization of military power and the glorification of war. Militarism can be observed in various aspects of society, including government policies, public discourse, and the allocation of resources. It played a significant role in the lead-up to World War I, as several European powers engaged in an arms race and adopted aggressive foreign policies, ultimately contributing to the outbreak of the war.

Lusitania:
The Lusitania was a British ocean liner that was famously sunk by a German submarine during World War I. The sinking occurred on May 7, 1915, off the coast of Ireland, resulting in the deaths of 1,198 passengers and crew, including 128 Americans. The incident significantly influenced public opinion in the United States and played a role in the eventual entry of the U.S. into the war. The sinking of the Lusitania highlighted the dangers of unrestricted submarine warfare and intensified anti-German sentiment.

Allied Nations:
The Allied Nations, also known as the Allies, were the countries that