Wikipedia:Summary style

Wikipedia articles cover topics at several levels of detail: the lead contains a quick summary of the topic's most important points, and each major subtopic is detailed in its own section of the article. The length of a given Wikipedia article tends to grow as people add information to it. Wikipedia articles cannot be of indefinite length as very long articles would cause problems and should be split.

World War II article in summary style
World War II

World War II ... was a global war that was underway by 1939 and ended in 1945 ....

Chronology

The start of the war is generally held to be 1 September 1939 ....

Background

World War I radically altered the political map, with the defeat of the Central Powers ....

Pre-war events
Italian invasion of Ethiopia (1935)

The Second Italo–Abyssinian War was a brief colonial war that began in October 1935 and ended in May 1936 ....

Spanish Civil War (1936–1939)

Germany and Italy lent support to the Nationalist insurrection led by general Francisco Franco in Spain ....

A fuller treatment of any major subtopic should go in a separate article of its own. Each subtopic or child article is a complete encyclopedic article in its own right and contains its own lead section that is quite similar to the summary in its parent article. It also contains a link back to the parent article and enough information about the broader parent subject to place the subject in context for the reader, even if this produces some duplication between the parent and child articles. The original article should contain a section with a summary of the subtopic's article as well as a link to it. This type of organization is made possible because Wikipedia is an online encyclopedia: unlike traditional paper encyclopedias, it only takes a click for readers to switch between articles, and there is no need to conserve paper by preventing duplication of content.

It is advisable to develop new material in a subtopic article before summarizing it in the parent article. (An exception to this is when the subtopic is non-notable; see below.) For copyright purposes, the first edit summary of a subtopic article formed by cutting text out of a parent article should link back to the original (see WP:Copying within Wikipedia). Templates are available to link to subtopics and to tag synchronization problems between a summary section and the article it summarizes.