Paul was deeply concerned over the condition of the believing community he left at Thessalonica. He and Silas had to leave in a hurry; indeed, they were expelled from the city by its ruling politarchs, who required Jason, whose home provided the necessary shelter for Paul and Silas, to post bond on their behalf to insure the peace of the city. Neither Paul nor Silas were legally able to return to the city as long as these same politarchs held office, which seems to be an annual term. However, the same magistrates could hold this office for more than one term, which would keep the evangelists out of the city even longer. Nevertheless, it seems probable that the security would have been returned to Jason, if no ruckus had taken place over a single term of office.
The believers at Thessalonica were struggling through a period persecution (2Thessalonians 1:4-5), which took a number of forms, some petty and some serious. One of the serious forms came by way of false brethren and/or false communication under the guise of a letter from Paul (2Thessalonians 2:2). It seems that the probable cause of the persecution came from the leaders of the synagogue who influenced the politarchs to take action against Paul and Silas in the first place (Acts 17:5-9). They may have planted false brethren in the believing community in order to influence their behavior and affect the message the believing community used to influence the gentile community of the city. One of the accusations the Jewish synagogue rulers made against Paul and Silas was they preached against the decrees of Caesar (Acts 17:7).
Paul showed some concern over spiritual words or messages (2Thessalonians 2:2), which seems to indicated an influence of a doctrine that was contrary to what Paul had taught the new believers (2Thessalonians 2:5) before he had to flee the city. The decrees of Caesar (Acts 17:7) under question included prophecy concerning the change or demise of any governing authority in the empire due to ill health etc. In 16 CE Tiberius Caesar issued such a decree, and such prophesies were also spread by Jewish authorities against Herod (see Josephus: Antiquities 17.2.4).
Paul had told them that the man of lawlessness would be exposed and judged by Jesus’ coming (2Thessalonians 2:8). This teaching may have been the focus of the enemy’s attention. The believing community at Thessalonica seems to have been influenced by false prophecy which may have come through false brethren and/or a forged letter from Paul (2Thessalonans 2:2). If believed and propagated by the believing church, they would have fallen into the trap of their enemies there, for not only would this violate the ‘peace’ bond posted by Jason (Acts 17:9), but such claims could also be used to substantiate their enemies claims that this new movement violates Caesar’s decrees.
This seems to have been the precarious position into which the new believing community at Thessalonica was placed by their enemies, and for this reason Paul in Athens was justifiably concerned (Acts 17:15; cp. 1Thessalonians 3:1-2). If the authorities in Thessalonica found reason to outlaw the Jesus Movement as a threat against the Roman Empire, this would create a precedent that would eventually put believers all over the empire at risk, for at present Rome saw no threat in the Messianic faith (cp. John 18:36-38).
For this reason Paul wrote 2Thessalonians (before writing 1Thessalonians, for the order in the NT is not according to the time Paul’s letters were written), reminding the church that the rebellion at Judea had to occur before the coming of Christ (cp. 2Thessalonians 2:3), but at the time of Paul’s letter the Roman government was holding back the man of lawlessness (cp. 2Thessalonians 2:6-7), keeping him from performing his will against the work of God in the Gospel. Paul saw the Roman government as a beneficial force and called for prayer for the emperor and all ruling authorities (1Thessalonians 2:1-2), seeing them as the ministers of God (Romans 13:6) for our good.
 See David W. Gill & Conrad Gemph: The Book of Acts in its First Century Setting; Vol. 2: Graeco-Roman Setting; Appendix: “The Politarchs” page 421.
 See Dio Chrysostom 57.15.8 cp. Dio Cassius 56.25.5-6