Blockchain technology has fundamentally changed decentralized networks by enabling the processes of consensus among distributed nodes. This is possible through consensus protocols that enhance the reliability, efficiency, and security of blockchain networks. This paper explains blockchain consensus mechanisms and how their components have evolved from PoW (proof-of-work) to many other, more efficient and low-power alternatives. This paper provides the issues with current Proof-of-Work (PoW) systems, including their high energy consumption and slow processing speeds. The study further examines advanced consensus mechanisms, such as Proof of Stake (PoS), Delegated Proof of Stake (DPoS), Byzantine Fault Tolerance (BFT)-based algorithms, and hybrid models, which are enhancing this area. Special attention is given to lightweight protocols specifically designed for Internet of Things (IoT) networks, with a focus on their scalability and computational efficiency. This overview paper examines the current state of long-lasting and user-centric blockchain solutions that consider the costs and benefits of security, scalability, and efficiency. The results provide a basis for understanding consensus mechanisms and spotting potential innovations in decentralized systems.