Justin Sun and Tron bought Steemit inc, which had a huge amount of STEEM. Along with that, J. Sun also own Poloniex with its share of STEEM. Recently, the Steem Witnesses created a softfork to protect the Steem Blockchain, but J. Sun went to the Exchanges and "borrowed" the Steem held by those exchanges for their clients in order to unseat our original witnesses and install his own. This then allowed him to undo the softfork and essentially hijack the Steem Blockchain. Now by the Steem Community voting for the original witnesses, the are slowly replacing or eclipsing the ones J. Sun placed. In a nut shell.

ps. now please vote for our witness, currently #1, #2, and #23 -40 or so.... but it could be changing so please verify. Thank you.