Is this still...

Yes I think that Jonestown is the largest mass suicide in modern history by a cult. The only mass suicides that surpass the Jonestown death toll came at the end of WWII in both Japan and Germany, Japan having the highest. In the battle of Saipan I think the death toll was around 5,000, where civilians chose to commit suicide rather than face defeat/capture by the Allies. Thousands of civilians committed suicide but this was over a period of time, not one large mass suicide where everyone died together at the same time, and no one forced or coerced them to do it, although I'm sure propaganda stories of what would happen to them if they fell into the hands of the Allies played a big part.

But like Bunnyshaped said, as far as the suicide cults like Waco, Heaven's Gate, Solar Temple, etc., where there's one single mass suicide where everyone dies together at the same time, none come close to Jonestown.

It really is mind blowing and scary, I think the isolation had a lot to do with it, once they were in Jonestown they were isolated from the outside world and the only news they were getting in was filtered through Jim Jones and his paranoia. He had his voice taped and played throughout the compound literally 24 hours a day telling them that the world is a bad place and people are out to get them and there's no way out. Plus a lot of people that joined People's Temple were feeling displaced and isolated from society in the first place (blacks and women trying to get equality in the 1960's and 70's) so I guess it was easier for Jones to play on their fears and brainwash them especially once he isolated them even more when they went to Jonestown.