Why is my video of a piece from Tchaikovsky's Op. 39 being blocked on youtube due copyright reasons?

So, I'm trying to download a video of me playing a piece - The Doll's Funeral - from Album for the Young by Tchaikovsky on youtube and it's been blocked. Does anyone know why a piece from 1878 is protected by copyright law? Or am I mistaken and this piece and the Children's Album, Op. 39 was not composed by Tchaikovsky? Tried to search on the internet and couldn't find an explanation.

Edit: Youtube has a disput option where I can claim the piece is in public domain. That'll probably solve the problem. Thanks