and impact of this network of internal border controls is controversial. B'Tselem, an Israeli non-governmental organisation that monitors human rights in Palestine, argues that they breach the rights guaranteed by the International Covenant on Economic, Social and Cultural Rights—in particular, the right to a livelihood, the right to an acceptable standard of living, the right to satisfactory nutrition, clothing, and housing, and the right to attain the best standard of physical and mental health. B'Tselem also argues that the restrictions on ill, wounded and pregnant Palestinians seeking acute medical care is in contravention of international law that states that medical professionals and the sick must be granted open passage. While Israeli Supreme Court has deemed the measures acceptable for security reasons, Haaretzs Amira Hass argues this policy defies one of the principles of the Oslo Accords, which states that Gaza and the West Bank constitute a single geographic unit. Much like relations between Jewish settlers in Israel and the native Palestinian population, strained intercommunal relations in Northern Ireland between Irish Catholics and the descendants of Protestant settlers from England and Scotland have resulted in de facto internal checkpoints. The peace lines are an internal border security measure to separate predominantly republican and nationalist Catholic neighbourhoods from predominantly loyalist and unionist Protestant neighbourhoods. They have been in place in some form or another since the end of The Troubles in 1998, with the Good Friday Agreement. The majority of peace walls are located in Belfast, but they also exist in Derry, Portadown, and Lurgan, with more than of walls in Northern Ireland. The peace lines range in length from a few hundred metres to over 5 kilometres. They may be made of iron, brick, steel or a combination of the three and are up to high. Some have gates in them (sometimes staffed by police) that allow passage during daylight but are closed at night. North America Multiple types of internal border controls exist in the United States. While the American territories of Guam and the Northern Mariana Islands follow the same visa policy as the mainland, together, they also maintain their own visa waiver programme for certain nationalities. Since the two territories are outside the customs territory of the United States, there are customs inspections when travelling between them, and the rest of the U.S. American Samoa has its own customs and immigration regulations, thus travelling between it and other