Editing Invasion (section)

==Defenses==
[[File:GreatWallNearBeijingWinter.jpg|thumb|The [[Great Wall of China]], built to defend China from invasion.]]

States with potentially hostile neighbors typically adopt [[defense (military)|defensive measures]] to delay or forestall an invasion. In addition to utilizing geographical barriers such as [[river]]s, [[marsh]]es, or rugged [[terrain]], these measures have historically included [[fortification]]s. Such a defense can be intended to actively prevent invading forces from entering the country by means of an extended and well-defended barrier; the [[Great Wall of China]], [[Hadrian's Wall]], and the [[Danewerk]] are famous examples. Such barriers have also included [[trench warfare|trench]] lines and, in more modern times, [[minefield]]s, [[closed-circuit television|cameras]], and [[motion detection|motion-sensitive]] [[sensor]]s.<ref>{{cite web|author=Defense Update|title=Accelerating the Kill Chain: Closing the Sensor-to-shooter Cycle|year=2006|url=http://www.defense-update.com/features/du-1-06/urban-c4i-7.htm|access-date=February 11, 2006|archive-url=https://web.archive.org/web/20060206010215/http://www.defense-update.com/features/du-1-06/urban-c4i-7.htm|archive-date=February 6, 2006|url-status=dead}}</ref> However, these barriers can require a large military force to provide the defense, as well as maintain the equipment and positions, which can impose a great [[economics|economic]] burden on the country. Some of those same techniques can also be turned against defenders, used to keep them from escape or resupply. During [[Operation Starvation]], [[Allies of World War II|Allied forces]] used airdropped mines to severely disrupt [[Empire of Japan|Japanese]] logistical operations within their own borders.<ref>{{cite web|author=Mason, Gerald A.|title=Operation Starvation|year=2002|url=http://www.stormingmedia.us/05/0560/A056024.html|access-date=February 11, 2006|archive-date=March 28, 2005|archive-url=https://web.archive.org/web/20050328150738/http://www.stormingmedia.us/05/0560/A056024.html|url-status=dead}}</ref>

[[File:Castle Church and Harbour.JPG|thumb|left|View from [[Dover Castle]].]]
Alternatively, the fortifications can be built up at a series of sites, such as [[castle]]s or forts placed near a border. These structures are designed to delay an invasion long enough for the defending nation to mobilize an army of a size sufficient for defense or, in some cases, counter-invasion—such as, for example, the [[Maginot Line]]. Forts can be positioned so that the [[garrison]]s can interdict the [[supply line]]s of the invaders. The theory behind these spaced forts is that the invader cannot afford to bypass these defenses, and so must lay [[siege]] to the structures.<ref>{{cite book|title=Fortress France: The Maginot Line and French Defenses in World War II|author1=Kaufmann, J.E. |author2=Kaufmann, H.W.|year=2005 |publisher=Prager Security International |isbn=0-275-98345-5}}</ref>

[[File:maginot line 2.jpg|thumb|upright=1.35|right|The view from a battery at Ouvrage Schoenenbourg in [[Alsace]]; notice the retractable turret in the left foreground.]]

In modern times, the notion of constructing large-scale static defenses to combat land-based threats has largely become obsolete. The use of precision air campaigns and large-scale [[mechanized warfare|mechanization]] have made lighter, more mobile defenses desirable to military planners. The obsolescence of large fortifications was displayed by the failure of the [[Maginot Line]] in the beginning of World War Two. Nations defending against modern invasions normally use large population centers such as [[city|cities]] or [[town]]s as defensive points. The invader must capture these points to destroy the defender's ability to wage war. The defender uses mobile [[armoured warfare|armored]] and [[infantry]] divisions to protect these points, but the defenders are still very mobile and can normally retreat. A prominent example of the use of cities as fortifications can be seen in the [[Military of Iraq|Iraqi Army]]'s stands in the [[2003 invasion of Iraq]] at [[Baghdad]], [[Tikrit]], and [[Basra]] in the major combat in the [[Iraq War]]. A defender can also use these mobile assets to precipitate a counteroffensive like the [[Soviet Union|Soviet]] [[Red Army]] at the [[Battle of Kursk]] or the [[Afghan Northern Alliance|Northern Alliance]] in [[Afghanistan]].{{citation needed|date=April 2014}}

However, static emplacements remain useful in both defense against naval attacks and [[anti-aircraft warfare|defense against air attacks]]. [[Naval mine]]s are still an inexpensive but effective way to defend [[port]]s and choke off supply lines. Large static air defense systems that combine antiaircraft guns with [[Transporter erector launcher|missile launchers]] are still the best way to defend against air attacks. Such systems were used effectively by the [[North Vietnam]]ese around [[Hanoi]]. Also, the [[United States]] has invested considerable time and money into the construction of a [[National Missile Defense]] system, a static defense grid intended to intercept nuclear [[intercontinental ballistic missile]]s.{{citation needed|date=April 2014}}

[[Island nation]]s, such as the [[United Kingdom]] or [[Japan]], and continental states with extensive [[coast]]s, such as the United States, have utilized a significant [[navy|naval]] presence to forestall an invasion of their country, rather than fortifying their border areas. A successful naval defense, however, usually requires a preponderance of naval power and the ability to sustain and service that defense force.{{citation needed|date=April 2014}}

In particularly large nations, the defending force may also [[withdrawal (military)|retreat]] to facilitate a [[counterattack]] by drawing the invaders deeper into hostile territory. One effect of this tactic is that the invading force becomes too spread out, making supply difficult and making the lines more susceptible to attack. This tactic, although costly, helped the Soviets stop the German advance at [[Battle of Stalingrad|Stalingrad]].<ref>{{cite web |author=Matters, James T.|title=Stalingrad&nbsp;– The Nazis Reach Beyond Their Grasp|year=2003 |url= http://home.carolina.rr.com/burntofferings/CHAPT11.htm|access-date=February 16, 2006 |archive-url=https://web.archive.org/web/20051226030308/http://home.carolina.rr.com/burntofferings/CHAPT11.htm |archive-date=December 26, 2005}}</ref> It can also cause the invading force to extend too far, allowing a [[pincer movement]] to cut them off from reinforcements. This was the cause of the British defeat at the [[Battle of Cowpens]] during the [[American Revolutionary War]].<ref>{{cite web |author=Withrow, Scott|title=The Battle of Cowpens|year=2005 |url=http://www.nps.gov/cowp/batlcowp.htm|access-date=February 16, 2006}}</ref> Finally, sending too many reinforcements can leave too few defenders in the attackers' territory, allowing a counter-invasion from other areas, as happened in the [[Second Punic War]].