This achievement requires you to reach Level 50, which is quite time consuming. It can be easily gained by upgrading your weapons and bases to their maximum levels and leaving them to do their thing by killing all the freaks.
A mission also gives you a helping hand with this achievement. The mission can vary from saving your neighbor, a supply truck or a ambulance to destroying stolen buses, cell cars or even a Goliath.
Sunburst is also a must when it comes to getting this achievement, but be warned if you are level 49 and near level 50, using it will prevent you from getting this achievement because it is currently glitched (this may be the same with level 9 to 10).