The Maurya empire succeeded the Nanda empire and was the biggest empire in India, and under Ashoka, it was also the biggest empire in the world at the time with an area of about 5 million square kilometers.
The Maurya empire was founded by Chandragupta Maurya under his advisor and strategist Chanakya. Chanakya is said to be the king maker who installed Chandragupta to the throne. There’s a story about both of them attacking the heart of the Nanda kingdom in Pataliputra and losing that battle.
They then retreated westwards to the mountains and Chanakya saw a little boy eating a hot roti from the edges. This gave him the idea that instead of attacking the heart of the kingdom they should attack the peripheries. They then formed alliances with some kings in the mountains, and slowly overthrew the kingdom. One of these kings is said to be Porus but there is no proof on who these kings actually were. Chanakya is said to have poisoned all the kings after they were victorious and thus Chandragupta became the absolute ruler.
Chandragupta was known as Sandrokottus to the Greeks, and there are Greek accounts which state that Sandrokottus even met Alexander the Great.
Chandragupta warred with Seleucus I Nicator who was one of Alexander the Great’s generals, and it seems very likely that Chandragupta won that war because of the terms of the treaty they signed. They concluded a marital alliance in which either Chandragupta or his son Bindusara married a Seleucus’ daughter, got vast areas (modern day Punjab and most of Afghanistan) that were ruled by the Greeks, and in exchange the Greeks got 500 war elephants. These elephants proved decisive in their victory in the Battle of Ipsus. Chandragupta left his successor a kingdom from Afghanistan to Bengal but it is not clear how much of the south they conquered.
Chandragupta was followed by Bindusara, who further expanded the kingdom southwards, and Bindusara was followed by Ashoka who was to be the greatest Indian emperor controlling an area which extended to almost all of India, and maintaining peace in the kingdom and diplomatic relations with the Greeks and the Egyptians.
Ashoka’s edicts are very well known now, but he was all but forgotten till the 19th century. British historians in India were finding pillars and rocks with a similar type of language all over India, but this language was not known, and therefore it was not known whether it belonged to the same king or to many different kings using the same language. Looking at a map of where all they were finding the edicts gives a sense of their original amazement as to who was this king that ruled such a vast territory.
Since, the language of these edicts was unknown, it wasn’t clear to them who was behind them and what was the message. This quandary was solved by James Prinsep. He was a scholar and orientalist who worked on deciphering and translating coins, edicts, rocks and manuscripts from all over India, and he was the one who translated Prakrit which was the language spoken during the time of Ashoka, and identified the ruler referred to “Devanampriya Piyadasi” which translates to “He who is the beloved servant of the Gods and who regards everyone amiably”. This post goes into great and fascinating detail about how these discoveries were made. An excerpt:
The image below shows the extent of Ashoka’s kingdom.
As you can see this is almost all of India except the extreme south. In fact it is more area than is under India today. The Maurya empire quickly disintegrated after Ashoka, and till the Britishers came in there was never a ruler who consolidated India like Ashoka did.