- Sweden: Denmark invaded Sweden multiple times throughout history, primarily during the 16th and 17th centuries. Notable conflicts include the Kalmar War (1611-1613) and the Torstenson War (1643-1645).
- Norway: Denmark and Norway were historically united under the Danish Crown, but Denmark did conduct military campaigns against rebellious Norwegian factions during periods of conflict.
- Schleswig-Holstein: Formerly a part of Denmark, Schleswig-Holstein became a point of contention between Denmark and Prussia, leading to the First Schleswig War (1848-1851) and the Second Schleswig War (1864).
- Estonia: In the 13th century, Denmark conquered and ruled over Northern Estonia, which later became part of the Livonian Order.
- Pomerania: Denmark had territories in Pomerania during the 12th and 13th centuries, as part of its control over the southern Baltic Sea region.
- England: During the Viking Age, Danish Vikings raided and sometimes established settlements in England, leading to conflicts and invasions such as the Danelaw period.
It is important to note that many European countries have a history of invasions and conflicts, and Denmark's involvement in military conflicts or invasions does not necessarily reflect the current state of its relations with other nations.