It seems easy to create a new galaxy, but really we did not know what a galaxy was, until a very few time ago. In the past, we didn’t have powerful observation instruments as today, so galaxies seemed small regions, placed everywhere in the skies and featured by a bright vagueness, called, exactly, nebulas.
Until the Twenties of the last century, scientists supposed that these nebulas were parts of our galaxy, whose real dimensions were still misterious. In 1924, astronomer Edwin Hubble, thanks to one of the most powerful telescope of his time, had been able to see some regions of the nebula of Andromeda, confirming that it was a single galaxy, external to ours. Already around 1929, Hubble discovered 18 galaxies, each one containing billions of stars.