Bitcoin is the crypto currency used for transactions in digital world. As anything in the digital world is can be copied and reused, bitcoins are designed in such a way that it uses consensus in a massive peer to peer network, so that the transactions carried using a bitcoin are irreversible. When a transaction is declared between two users the miners would check the transaction list of the first user in order to make sure that the bitcoin used in the present transaction is not used in any previous transactions. The information of the bitcoin usage is sent to all the contact nodes of the first user for confirmation and getting confirmation from all nodes the transaction will be done to the second user. The confirmation is always solved by miners and recorded as a block and maintains the long blockchain.
For such maintenance and updating the transactions miners will be rewarded with bitcoins. These are carried out by a pool of miners and the network can be successfully carried by an honest pool of miners. One dishonest miner can collapse the concept of bitcoins by stimulating the hashing power. The larger pools always get centralized by the pool server maintained by a miner manger which goes against the basic concept of bitcoin news system of decentralization; if the miner manager becomes dishonest the system can be manipulated with available sources and to the downfall of the bitcoin exchange value. By facing such situations and to regain the basic concept of bitcoins a new fork is introduced by Satoshi called as bitcoin.
As some of the larger mining pools misused the concept of bitcoin blockchain by using ASICs (Application Specific Integrated Circuits) in mining rather than GPU (Graphical Processing Unit)and engaged into abusive practices against individual miners in order to regain the basic concept one CPU one vote by Satoshi they started a new chain to the existing blockchain called bitcoin.