The rapture is after the Great Tribulation has ended, after Christ's second coming begins, after the resurrection of the dead in Christ.
1Th 4:13 But I would not have you to be ignorant, brethren, concerning them which are asleep, that ye sorrow not, even as others which have no hope.
1Th 4:14 For if we believe that Jesus died and rose again, even so them also which sleep in Jesus will God bring with him.(second coming reference)
1Th 4:15 For this we say unto you by the word of the Lord, that we which are alive and remain unto the coming of the Lord (second coming reference) shall not prevent them which are asleep.
1Th 4:16 For the Lord himself shall descend from heaven (second coming reference) with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: (the resurrection of the dead in Christ)
1Th 4:17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord. (the rapture)
The resurrection only happens at the second coming and the second coming can only happen after the trib has ended, and since the verses tell us the rapture happens AFTER the resurrection and second coming means these verses decisively prove the rapture is post-trib not pre-trib.
It's that simple.
Christ also spoke of the rapture but used the wording of saints being gathered together, and no surprise, placed it after the end of the Great Tribulation.
Mat 24:29 Immediately after the tribulation (great tribulation has ended) of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken:
Mat 24:30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming (second coming reference) in the clouds of heaven with power and great glory.
Mat 24:31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect (*another way to speak of the Rapture) from the four winds, from one end of heaven to the other.
*(also see 2nd Thessalonians 2:1 for the same language regarding the Rapture)
Timing of the gathering/rapturing is exactly the same in these two passages. In both we have saved Christians being moved from one place to another and in both that happens after the tribulation has ended and when the second coming has commenced.