Why do galaxies form clusters?

Galaxies form clusters due to the gravitational attraction between them, which pulls galaxies that are relatively close together into groups. Over time, these gravitational interactions can lead to the merging of smaller clusters into larger ones. Additionally, the presence of dark matter plays a crucial role in providing the necessary gravitational framework to hold these clusters together. Clusters are often located in regions of higher density in the universe, where the overall gravitational pull is stronger.