The term the 'grey-zone' is relatively new to the military lexicon however, it is having a significant impact among strategists. Of particular interest are the activities by China and Russia, among others. Examples include the Russian annexation of Crimea and Chinese island-building in the South China Sea. Conventional military forces find it very difficult to counter such strategies, as they remain below the traditional threshold for a response. For example, a fishing boat might be just a fishing boat however, it could also be crewed by members of China's PLA maritime or militia forces. Reading this article (p.41) is an excellent way to start engaging with the concept of hybrid and grey-zone warfare and how it is shaping military strategic thinking. The article goes so far as to suggest that Chinese-Russian cooperation in the grey-zone could undermine the US as the guarantor of the rules-based order.