ARPANET was the first network established by the U.S. Defense Department in the 1960s during the Cold War to enable communication between computers and allow for alternative routes in case of damage. The main goals of computer networks are resource sharing between computers, high reliability through alternative data sources, security, providing a powerful communication medium, and scalability through adding more processors. Computer networks enable applications like e-commerce, remote access, electronic commerce, and home automation applications. The key components of a computer network include hardware like network interface controllers, servers, clients, transmission media, routers, bridges, hubs, switches, gateways, and repeaters. Software and cables/connectors are also essential network components.