How is intervention different from mutual war?

It differs in that an enemy state interferes in the internal affairs of a country where there is a civil war or political instability. Something similar happened in Russia during the years of turmoil, when Poland tried to seize control of the state with the help of military force. But despite the internal split and the strength of the enemy, the Poles were still driven out. So the time of troubles ended, which brought many troubles to the Russian people.