An attempt to predict the capability or weapons that will decide future wars is almost impossible in this fast changing world considering the fact that an ability that has its place at the pinnacle of technological innovation may be considered obsolete is no distant time due to another ability that successful counters it or environmental issues.
Also the nature of war is not constant but fluid and an ability that may be a game changer in a conventional war between two country may be useless or cost effective in a smaller conflict or assymmetrical scenario pitting force in an urban theater. (e.g Nigeria Army confronting Niger Delta militant or Boko Haram insurgents).
However, this capabilities and abilities will be very pivotal in future battle and will change the very nature of future warfare.

(1) STEALTH CAPABILITIES: Using naturally occurring metamaterials, scientists have been designing lightwave-bending materials that can greatly reduce the thermal and visible signatures of a target. This ability will be game changer in future conflict. They represent the pinnacle of technological weapons sophistication and are the bleeding edge of innovation.
The ability to record low radar signature has been used by many countries on high sea assets like warships and submarines but this capability is still an exclusive capability in air assets as only U.S and China have operational military hardwares with stealth capabilities. The U.S F22 and F35 Fighter Jet and B-2 Spirit and F-117 Nighthawk Bombers and the Chinese newly commissioned J-20 are the only operational air asset with stealth capabilities although their are many more aircraft with stealth capabilities still in experimental stage in different countries. Stealth suit for land soldiers are also being experimented by some military.
Chinese Shenyang J-31, Japanese Mitsubishi X-2, Russian PAK-FA-T-50 and Swedish Stealth Saab Gripen are the known aircraft currently at the operational stage. Also Stealth capabilites is being experimented on Main Battle Tanks and Poland is currently pushing the innovation on its concept tank PL-01. How well a country can evade enemy radars and eyes will be game changers in future conflicts.

(2) Cyber Space Capabilites: Apart from the three conventional domain being used in warfare which are, Land, Sea and Air, future wars will be fought on two additional domains. Outer Space and Cyberspace will also be battlefields in future wars.
Cyber war will see hackers wage war against each other for the control of cyberspace but this won't be them stealing facebook user info or hacking email but they will be working to takedown modern military nervous system and stuxnet-style digital weapons.
Cyberspace battle will be targeting computers and networks in warfare, communication and internet connection systems, military installations, and other important assets and installation in offensive and defensive operations.
New breed of military equipment and bots using artificial intelligence will also attack and defend in cyber war by automating work like probing and targeting enemy network or crafting fake information.

(3) Speed: Speed increases the element of surprise and enhance the potency of attack and ability to evade countermeasures...

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