Early in the XIX century, the founders of glacial theory conceived of a "polar ice cap'' centered on the North Pole and extending as far south as central Europe. However later this model was discarded. The deep Arctic Ocean, discovered in 1890s, was thought inconsistent with the model. Moreover, a belief took hold that the Arctic was not more severely glacierized than now, as polar snowfall seemed insufficient to nourish much bigger ice masses. So the reigning concept of the XX century suggested that the past great ice sheets of Northern Hemisphere had mostly located on the mid-latitude continents. This concept was first challenged in 1970s, when Hughes et al. 1977 put forth the model of an Arctic Ice Sheet AIS that had formed largely in the Arctic Ocean. A core ice-shelf mechanism of Arctic Ice Sheet formation was proposed, which suggested: first, an inception of ice shelves in confined cold-water seas; second, turning the ice shelves into marine ice domes grounded on the polar continental shelves; and third, amalgamation of the Arctic terrestrial, marine-based, and floating ice components into a single Antarctic-style dynamic system. Now, a marine ice transgression hypothesis is proposed which suggests that the Arctic marine ice domes and thick floating ice shelf would push outwards and transgress onto adjacent lands. The Arctic Ice Sheet was an unstable, threshold-like system, prone to generate nonlinear responses to gradual change in forcing. The responses materialized in glacial surges, Heinrich events, and megafloods. As a result of the Earth's rotation, the system developed a west-to-east asymmetry.