The Huns drove them out of their lands. The Goths needed to find better lands to support their population. The Roman Empire was weak. The Romans had better land. The Romans couldn't defend their land against the Goths and the Goths couldn't defend their lands against the Huns.

As for the climate change argument this movement of people groups is not uncommon. Rome up until the arrival of the Goths had been dealing with "barbarian" incursions for a thousand years.

Rome invade Gaul, Germany, and Britannia which people seem to omit. There is no argument that climate change forced them too. They did it because they could. The "barbarian" tribes invaded because they could. Both sides in this conflict are human and have human motivations.

I was wondering the same things : I often heard that the relative civilizational collapse that happened in europe during the middle ages was correlated with lower overall temperatures, e.g. what you see here [1] or there [2]. In the second one, the most recent projections (in red), show that there were a lot of very cold years (down to -0.6 degrees relative to normal) during those times. Later on, starting in the 1200s, there was the Little ice age, where temperatures fell to -0.9 relative to normal (I don't know how they defined normal). The peak, when almost all years were at -0.6 or below on that scale, caused the "General Crisis of the seventeenth century" where people from the Goth/scandinavian regions also had huge famines [3].

So my guess would be that there were several very cold years in a row, which caused famines, and the populations understood that their best survival chance was to migrate south, where they had to compete with the roman empire for land.

[1] https://fr.wikipedia.org/wiki/Fichier:2000_Year_Temperature_... [2] https://fr.wikipedia.org/wiki/Fichier:2000_Year_Temperature_... [3] https://en.wikipedia.org/wiki/Great_Famine_of_1695%E2%80%931...

I was visiting the northern city of Umeå in Sweden, in the middle of the winter. It's a bit dark, and in a good year you get a mantle of snow that reaches waist-high, and that was a good year. So I'm sitting in this super-cozy fika room with nice warm lighting having some coffee. Out of the blue, this sweet middle aged lady who had been born there a good half a century before and who loves skiing, says: "I can't bear the darkness any longer. I'm going to Spain this year."

Overpopulation, Scandinavia did not have very fertile soil.