Sauron's Empire was the first inter-galactic empire following the Second War of the Republic of Palpatine.
After the Second Republic War ended in year 2782, the Dark Lord Sauron of Cartwheel Galaxy (yes the same Sauron as The LoTR) built a great army with the help of his allies, the Easterlings and the Haradrim, of advanced Orcs and Men and other dark creatures, hoping to build an empire. He waged war on the Republic, which was weakened and could not defeat him. At the Treaty of Anrot-93, Sauron annexed a region of 100 million light-years around the Cartwheel Galaxy from the Republic. This was known as the Grand Mordorian Empire officially.
The armies of Sauron were the greatest in strength and advancements, with Sauron currently having over 100 million orcs, 50 million from Mannish allies and 10 million other creatures. Sauron also commands the greatest research factories in the universe and has over 100 million ships that have faster-than-light and wormhole abilities. A lot of Sauron's military strength remains a secret, however.....
Sauron has many enemies, including the Republic and the Empire of Voldemort (don't blame me for defeating him in a vs. Sauron), the latter now expected to fight a war to decide who was the greater Dark Lord.