The collision of galaxies is very common in the evolution of the universe.
Due to the extremely tenuous distribution of matter in the galaxies themselves, these collisions are not in the normal sense of the word, but gravitational interactions.
The collision may lead to fusion. This occurs when two galaxies collide and do not have enough strength to continue traveling after the collision. Instead, they attract each other, returning back and eventually merge, after several passages through, forming a single galaxy. If one of the clusters in collision is much larger than the other, it will remain intact after the fusion, that it means that the largest galaxy will look the same, while the smaller galaxy is removed and become part of the large one.