In the US there have only been two extensions of copyright terms since Disney came into existence.

The first was in 1976, as part of a major overhaul of US copyright law to update the previous law (from 1909) to take into account the large changes in technology since then, and to make US law work more like the rest of the world to pave the way for the US later joining the Berne Convention. The changes for Berne compatibility included longer terms.

I assume Disney did support this, but only because as far as I can tell it had pretty widespread support. It had enough support that it would have passed even if Disney had adamantly opposed it.

The second was in 1998, and that was specifically a term expansion (as opposed to a term expansion like that of 1976 that was a side effect of harmonizing US law with the rest of the world). Europe had expanded terms a few years earlier, so the 1998 change in the US might have been motivated at least in part by harmonization, but I don't think the differences in terms between the US and the EU would have been enough to get it passed without some major interests pushing for it, so it is probably fair to give Disney a good part of the credit or blame for this one.