Compare this with Islam. All those conquest was definitely for religion. Unlike Christianity which mainly spread among the lower-class peacefully (heck, they were even fed to lions or impaled and burned on stakes), Islam was spread by the sword, with the army led by no other than Muhammad himself.
And oh, Catholicism came later during the Great Schism.
There is not a single country which has voluntarily accepted Islam. In all the nations, Islam was spread using force and genocide. Even now, the same is ongoing, in nations such as Sudan and Pakistan.