The U.S. states that remained in the existing Union during the American Civil War. When referring to the Northern United States in this context, it is common to use the shorter form "The North" (contrasting with "The South" which most often refers to the southern states which declared secession). Which states the historical "North" actually comprises in this context is the subject of some minor disagreement. Those states which did not permit slavery are almost always included in this grouping, while some slave-holding states that remained in the Union (such as Maryland and Missouri) are often excluded. Additionally, some states which are occasionally counted as "northern" in this context are not necessarily located in the geographic north. The U.S. states of California and Kansas, for example, are sometimes included in this historical grouping, although neither state is entirely geographically "northern".