A system may include a transaction history controller to store, in a distributed blockchain database, a first chain including a primary head node for a first subscriber to a social media history map service and multiple blocks each representing an online transaction for the first subscriber, and a second chain including a follower head node, linked to the primary head node, for a second subscriber and multiple blocks each representing an online transaction for the second subscriber. The transaction history controller may receive data representing a first online transaction for the second subscriber, format the data for the distributed blockchain database, store the formatted data as a new block in the second chain, receive a request to generate a trend report for a cluster of subscribers that includes the first and second subscribers, and generate the trend report dependent on the blocks in the first and second chains.