Please answer a question about the following article about Roman Republic:

Mithridates the Great was the ruler of Pontus, a large kingdom in Asia Minor (modern Turkey), from 120 to 63 BC. Mithridates antagonised Rome by seeking to expand his kingdom, and Rome for her part seemed equally eager for war and the spoils and prestige that it might bring. In 88 BC, Mithridates ordered the killing of a majority of the 80,000 Romans living in his kingdom. The massacre was the official reason given for the commencement of hostilities in the First Mithridatic War. The Roman general Lucius Cornelius Sulla forced Mithridates out of Greece proper, but then had to return to Italy to answer the internal threat posed by his rival, Gaius Marius. A peace was made between Rome and Pontus, but this proved only a temporary lull.

How did the ruler of Pontus anger Rome?
by seeking to expand his kingdom