Respuesta :
Austria-Hungary had invaded Serbia, and Russia was in an alliance with Serbia.
The Russians decided to send troops to the border to Austria-Hungary in 1914 because Austria-Hungary had invaded Serbia, and Russia was in an alliance with Serbia.
In the beginning of the first World War:
- Austria-Hungary invaded Serbia
- Russia went to war with Austria-Hungary to protect Serbia
Russia and Serbia had signed a treaty that stated that Russia would defend the Serbians if they were attacked so when the Austrians attacked, the Russians sent troops to fight Austria.
In conclusion, Russia sent troops to defend Serbia.
Find out more about World War I at https://brainly.com/question/2628215.