The XRP blockchain is centralised
There are many validators already running. You can configure the validators to trust using a [Unique Node List](They are the lists of transaction validators a given participant believes will not conspire to defraud them.) (UNL).
Regardless: everyone can run a rippled
node and/or validator and introduce transactions: if the transaction is valid (signed, etc.) it's guaranteed to be included.
Ripple is working on further decentralization.
Read more on the decentralisation strategy
Check this article for an educating read 🎉