All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallAllaahu 'alayhi wa sallam, is His Slave and Messenger.
Allaah Almighty is the Lord; He says (what means): {[All] praise is [due] to Allaah, Lord of the worlds.}[Quran 1:2] He is the Lord and the Creator of the universe. The whole universe is under the full control and power of Allaah. He is able to do all things. He uses whatever and whoever He wishes to do whatever He wishes whenever He wishes. In this sense, the whole universe can be referred to as "the soldiers of Allaah."
Allaah may even employ a disobedient and wicked person, who will have no share in the Hereafter, to support His religion. The Prophet said: "Allaah may support this religion (i.e. Islam) even with an impious man."
The term "the soldiers of Allaah" may also refer to a special category of His creation. For example, Allaah says (what means): {...And none knows the soldiers of your Lord except Him. And mention of the Fire is not but a reminder to humanity.}[Quran 74:31] The context of this verse is about the angels as it talks about the keepers of Hellfire from among the angels. Al-Qurtubi commented on the verse: "The verse means that only Allaah knows the exact number of the angels whom He created for carrying out the punishment on the people of Hellfire."
Also, the expression "soldiers of Allaah" includes, besides the angels, all the slaves who believe in Allaah and strive to defend and support His religion and raise the banner of Islam and the Word of Allaah.
Allaah knows best.