The military concept of delaying or preventing opposing forces from capturing a specific area is as old as war. The focus is typically on naval and aerial operations that establish tactical superiority, but ground operations tend to have more numerous and lower-cost platforms. Area denial efforts on the ground have an incredible effect on the conduct of modern warfare, especially in recent hybrid conflicts.
Rather than establishing complete physical control over a particular position, the concept of anti-access and area denial focuses on making a location off-limits to the enemy, thereby forcing enemy fighters into terrain of the defenders' choosing. Those defenders can then concentrate and allocate forces favorably, gaining superiority. This can often be achieved with little cost in terms of time, equipment and men. Anti-access and area denial is a critical strategy often used by weaker forces against stronger ones, because preventing the enemy from taking and holding a particular area is often easier than controlling it.
To be effective, area denial efforts do not necessarily need to halt or drive out opposing forces entirely. By inflicting intolerable losses or by funneling opposing forces to selected areas, defensive ground forces can be more efficiently deployed along the gaps in these areas, blocking the best avenues of approach and raising the cost for enemy fighters to traverse them. Area denial can also be an effective way to disrupt the establishment of capable logistics nodes that support further advances by combat elements.
Tactics and weapons that deny terrain or delay opposing ground forces will continue to be prevalent in modern warfare. In the fight against the Islamic State in Iraq, U.S. forces have consistently applied the anti-access concept, denying the use of ridgelines and hilltops to Islamic State fighters. Likewise, the militant group is itself adept at using improvised explosive devices and a handful of mobile sharpshooters to prevent Iraqi forces from taking ground from them.