The blockchain technology has gained significant popularity among different users around the world by promising them a fully decentralized network independent from trusted third parties, governments or other central authorities. Instead of trusting a single instance, the trust is distributed among a large group of people, that validate transactions and add those to the blockchain. This process, referred to as mining , has experienced trends of centralization, possibly presenting a major threat to the security and usability of blockchains. So far there is only a limited understanding of the mechanisms behind centralization of mining power. To better understand the underlying mechanisms, we investigated the major Proof-of-Work blockchains (B...