If Salahdin waited for a chance and didn't fight, we wouldn't have access to Al Aqsa for the last 1000 years.
Islam is not a pacifist religion, we have conditions under which warfare is acceptable. Just look at the life of Prophet PBUH. If we were only supposed to wait for Allah's help, then Allah would have instructed us so in Quran. Instead we see Allah commanded to fight against oppressors. The help in Badr only came after Muslims went to battlefield. They were not hiding in caves while the angels fought the Kuffar.
Abu Bakr reported: The Messenger of Allah, peace and blessings be upon him, said, “Verily, if people see an oppressor and they do not seize his hand, Allah will soon send His punishment upon all of them.”
Source: Sunan al-Tirmidhī 2168
Grade: Sahih (authentic) according to Al-Albani
Bottom line - we cannot sit back and watch the show while people are being oppressed.