Weytahn from orbit
Weytahn is the name given by the Andorians to a formerly uninhabitable Class D planetoid, approximately as large as Earth's moon. It is the home to a rather pernicious mutagenic pathogen that is capable of harming Humans, but does not affect Vulcans. Weytahn is located on the frontier between the Vulcan system and the Andorian Empire. Both sides claim it belongs to them, having nearly gone to war over the planetoid twice.
Weytahn was terraformed by the Andorians in the 2050s for the purpose of establishing a colony there. Once an atmosphere was developed, they established a settlement. Due in part to its relatively close proximity to Vulcan territory, Weytahn was believed by the Vulcan High Command to be a covert military installation.
An Andorian and a Vulcan ship in orbit of Weytahn in 2152
An Andorian map of the surface (upside down)
In 2097, Weytahn's peaceful settlers were forcibly removed and placed in refugee camps; the planet was then annexed by the Vulcans and renamed as Paan Mokar. A surveillance satellite was put into orbit to monitor the agreement, known as the Territorial Compromise (or Treaty of 2097). This agreement, which the Andorians referred to as oppressive, was a 1,200 page document and took eight years to work out.
Weytahn remained deserted until 2152, when Shran, an Andorian regimental commander, landed a force on the planetoid and occupied the settlement in an attempt to forcibly rescind the Compromise. The Vulcans attempted to enforce the Treaty of 2097 and managed to regain control of half of the colony. They, however, suffered several causalities, including two dozen wounded and three taken hostage. Shran agreed to discuss terms for their safe return, but only if Jonathan Archer would act as mediator. Archer was able to get the two sides together and establish a common goal for the two sides to work towards. (ENT: "Cease Fire")
The Vulcans eventually agreed to cede ownership of the world to the Andorians. When High Command Administrator V'Las planned an invasion of Andoria, the Andorians were tricked into believing the Vulcans would attempt to retake Weytahn, thereby committing much of their fleet to that world and leaving Andoria vulnerable. (ENT: "Kir'Shara")