Thessalonica is the largest city in the Macedonia region.
It was a region where many Jews lived, to the extent that there was a Jewish synagogue. Paul preached the gospel in this region, focusing on the synagogue. While many Greeks accepted the gospel, the Jews, on the other hand, strongly opposed it and caused a disturbance.
Acts 17:1Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where there was a synagogue of the Jews.Acts 17:2Then Paul, as his custom was, went in to them, and for three Sabbaths reasoned with them from the Scriptures,Acts 17:3explaining and demonstrating that the Christ had to suffer and rise again from the dead, and saying, “This Jesus whom I preach to you is the Christ.”Acts 17:4And some of them were persuaded; and a great multitude of the devout Greeks, and not a few of the leading women, joined Paul and Silas.Acts 17:5But the Jews who were not persuaded, becoming envious, took some of the evil men from the marketplace, and gathering a mob, set all the city in an uproar and attacked Jason’s house, and sought to bring them out to the people.Acts 17:6But when they did not find them, they dragged Jason and some brethren to the rulers of the city, crying out, “These who have turned the world upside down have come here too.Acts 17:7Jason has harbored them, and these are all acting contrary to the decrees of Caesar, saying there is another king—Jesus.”Acts 17:8And they troubled the crowd and the rulers of the city when they heard these things.
It was here that they first earned the title "those who have turned the world upside down."