90. Why is the word jihad applied to the battles of the early Muslims?

Because these battles had to be fought for the very existence of the religion of Islam, and because the Muslims had to strive hard by risking their lives and by sacrificing their possessions. Taking part in these battles was a great struggle, done only to save Islam from destruction and no other reason. 

Before their emigration (hijra) to Madina, while living in Makka, the converts to Islam had to face terrible persecution and torture. But they bore it all with patience. In the Quran this was also called a jihad on their part. After the Muslims had been forced to emigrate to Madina, the opponents of Islam in Makka decided to wage war upon them. So the Muslims then had to fight battles in self-defence. As they had no proper army or equipment, each member of the Muslim community had to do, and to give, all that he or she could. They volunteered to fight in the battles, and gave their money and possessions for the war. Therefore this was called a jihad by means of one's life and property.