This article What is a Demon? by Fr. José Antonio Fortea Cucurulla, a Spanish writer, and a Roman Catholic priest and exorcist of the diocese of Alcalá de Henares (Madrid), speaks of what the angelic fight, a fight between spiritual beings, was all about:
Now war arose in heaven, Michael and his angels fighting against the
dragon; and the dragon and his angels fought, but they were defeated
and there was no longer any place for them in heaven. And the great
dragon was thrown down, that ancient serpent, who is called the Devil
and Satan, the deceiver of the whole world—he was thrown down to the
earth, and his angels were thrown down with him (Rv 12:7-9).
How can purely spiritual beings fight among themselves? What weapons
do they use? Angels are spirits, so their battles must be purely
intellectual. The only weapons that they can use are intellectual
arguments. The angels gave reasons to the rebels for why they should
return to obedience to God. The rebel angels countered with their
reasons to support their position and spread their rebellion among the
faithful angels. In this epic angelic battle, some who were inclined
to rebel returned to obedience, while some of the faithful angels were
seduced by the evil arguments of the rebels.
From above we see that God had asked or commanded the angels to do something. The dragon and his angels rebelled and did not want to obey and tried to instigate others to join in the rebellion with St. Michael (From the Hebrew name מִיכָאֵל (Mikha'el) meaning "who is like God?". This is a rhetorical question, implying no person is like God) and the faithful angels countering with their arguments.
Revelation tells us that a third were not faithful and were kicked out of heaven and became the demons, the Devil or Satan and his angels.
As regards winning, the good side always wins (in the end) i.e. God's side always wins and he is the one who provides the victory.
Rev 12:9-11 (RSVCE) 9 And the great dragon was thrown
down, that ancient serpent, who is called the Devil and Satan, the
deceiver of the whole world—he was thrown down to the earth, and his
angels were thrown down with him. 10 And I heard a loud voice in
heaven, saying, “Now the salvation and the power and the kingdom of
our God and the authority of his Christ have come1, for the accuser of
our brethren has been thrown down, who accuses them day and night
before our God. 11 And they have conquered him by the blood of the
Lamb and by the word of their testimony, for they loved not their
lives even unto death.
1. The Jerusalem Bible Popular Edition renders this: Victory and power and empire for ever have been won by our God