It is common to think of Paul as having three missionary journeys which all begin from Antioch. This is not actually the way the book of Acts structures Paul’s ministry.
Verse 5 says: “So the churches were strengthened in the faith, and they increased in numbers daily.” This, or something like this, is used in Acts as a section marker. It occurs after every major movement in Acts especially as the gospel has reached an area and before it begins a new section.
Rather than three missionary journeys Paul has a mission in Asia, a mission around the Aegean Sea and finally a mission to Rome. The account of the mission to Asia begins with the Holy Spirit’s direction in Acts 13:1 and concludes with Acts 16:5 as above. The Jerusalem Council is part of the expansion of the gospel to Asia. Generally, the pattern is a gospel visit to the churches and then a second visit to strengthen the churches. Therefore in 15:36 Paul suggests to Barnabas, “Let us return and visit the brothers in every city where we proclaimed the word of the Lord and see how they are.” Paul and Barnabas argue about taking Mark (author of the gospel) with them because he had earlier deserted them. Barnabas wanted to give him a second chance. Paul was wrong as became apparent later on. Due to their disagreement Barnabas took Mark and returned to Cyprus and Paul took Silas and returned to cities mentioned earlier in Acts 13-14. Note how it says: And he went through Syria and Cilicia, strengthening the churches.
So, the Council of Jerusalem falls mid-way through the mission to Asia – after the initial evangelization visit and before the second strengthening visit. As they went on their way through the cities, they delivered to them for observance the decisions that had been reached by the apostles and elders who were in Jerusalem. With the dangers avoided the section concludes: “So the churches were strengthened in the faith, and they increased in numbers daily.”
Next Acts will recount Paul’s mission around the Aegean Sea as the gospel expands to the ends of the earth. It will begin with a new direction from the Holy Spirit as happened in the Asian mission. Not three journeys but three gospel expansions among the Gentiles paralleling the expansion of the gospel among the Jews – Jerusalem, Judea and Samaria.