Question

9. Once the first declaration of war was made and the alliance system began to kick in, what other countries became

involved?

Answer 1

Austria-Hungary made first declaration of war against Serbia. An alliance system called the allied powers started to kick in United States, China, Soviet Union, France, Great Britain.

Step-by-step explanation:

Because of assassination of the Austrian Prince Francis Ferdinand and his wife Sophia on June 28, 1914.