Each era represents a slice of time within the Battletech Universe. During the flow of time factions and units will appear or disappear and some just change with the times.
2005 - 2570
2571 - 2780
2781 - 2900
2901 - 3049
3050 - 3061
3062 - 3067
3068 - 3080
3081 - 3130
3131 - 3999