Word studies simply aren't enough. Amos, as with all the prophets, is bringing a Covenant lawsuit against those whose fathers swore to keep Covenant with God. God would quite justly bring disaster upon them because He told them exactly what He would do to them (see Lev 26 and Deut 28 for Covenant blessings and curses).
What is more, the text even tells us that the Lord tells the prophets exactly what He was going to do. They are his "repo men," knocking on the door with words from the landlord.
In the New Testament, it is the apostles who take on this role. Acts and Hebrews and Revelation make perfect sense in light of this Covenantal understanding. The apostles were blowing the trumpets around the city, and the last trumpet would bring upon it all the innocent blood of the prophets beginning with Abel.
So, direct causation, yes. Via Assyria, Babylon and Rome, but direct nonetheless, as per the contract.