Such a practice is known as shifting cultivation or slash-and-burn. This was used by tribal people and American Indians for farming. They clear the land, grow crops for a few years, and move away when the land is fallow, allowing the land to regain nutrients and the forest to grow back. They generally return to the land in 10 to 12 years.
<em>Anoxia, or a lack of oxygen in bodies of water leads to</em> dead zones.
Roman Catholicism is the dominant religion of western europe
Near the coast you have smaller seas, but I think the Pacific Ocean is the one you are looking for.
