Whilst im doing an essay on the Martial Race Theory, might as well have a try and answer this question for you. Do note that this is my first time answering a question and my sources are mainly British made primary sources, so take that to heart.

Ranjit Singh’s Empire at its greatest extent spanned a large part of the Geographical Punjab.

This is a map of the Punjab Region: http://www.sikharchives.com/wp-content/uploads/2011/03/sikh_empire_map.jpg

Imagine then, from the foothills of the Hindu-Kush to the Sutlej River (The easternmost tributary of the Indus) and from Multan to foothills of the Himalayas the Sikh Kingdom of Ranjit Singh held great influence. East to the Sutlej were the Cis-Sutlej states, a collection of various small kingdoms that came under British influence in the early 1800’s, a fact that brought no small amount of concern to Ranjit Singh (though he maintained a friendly relationship with them throughout his rule). West of them was the Kingdom of Afghanistan which made a hobby of raiding and plundering the Punjab, though not so much anymore when Ranjit Singh established the Sikh Kingdom.

Now, you ask if there have been any other Sikh Empires larger than his? Well, his was really the only Sikh Empire to have existed. By Empire here I mean something that can be recognized as an organized state that administers and hold sway over recognized territory. I say this because the Sikh Empire of Ranjit Singh wasn’t what we would immediately call an empire with centralised authority and beurocracy, it was rather a collection of statelets and confederacies held together by the person of Ranjit Singh.

See, the Punjab region before the coming to power of Ranjit Singh was a turbulent and chaotic place. Once the Gateway of the Mughal Empire to the Middle East the region in the 18th Century broke away from Mughal administrative rule and the Punjabis established various stateless, made confederacies and had some tribes sprinkled around. Naturally a breakdown of central authority resulted in a bit of chaos. Raiding and intercene warfare was commonplace. For the Sikhs they establish various Misl’s (other spellings include Misals or Misuls), sovereign states that banded together under the Sikh Confederacy in 1769. However this was a unity against outsiders, they still competed against each other for land and other resources.

Joseph Davey Cunningham had this to say on the Sikh Confederacy: “The Sikhs had become a nation, and in theory a united Nation, but in actual fact such was far from being the case. The new State was composed of a number – twelve is the usually recognized total- of leagues or ‘Misals’. Instead of uniting and forming a solid State, these ‘Misals’ were almost constantly engaged in civil war, grouping and regrouping in the struggle for pre-eminence”

Until Ranjit Singh came along and, primarily with military might, brought the Sikh Confederacy, and eventually most of the Punjab, under his heel. After his death, the empire he built, that centred around his person, did not have a strong successor and the very army that had won him the state turned to its own interests. In 1845 this army crossed the Sutlej, attacked and occupied British-protected territory and began the First Anglo Sikh War which would see the Sikh Empire lose territory (Though not before giving the British a good run for their money). The Second Anglo Sikh War in 1848-49 resulted in the final annexation of the Sikh Empire.

Sources:

Cunningham, Joseph Davey. "A History of the Sikhs" (Oxford, Oxford University Press, 1918)

Griffin, Henry Lapell. “Rulers of India: Ranjit Singh” (Oxford, Claredon Press, 1892)

G.F MacMunn, “The Armies of India”, (London, Adam and Charles Black, 1911)

Holmes, Richard. “Sahib: The British Soldier in India, 1750-1914” (Harper Collins, London, 2005)