#denfra

in the Early Middle Ages, big political shifts in France or Denmark usually resulted in someone invading and trying to conquer England. the Viking Age itself likely started due to Frankish expansion on the continent, which pushed the Danes to consolidate a more centralized government in Denmark, and the people who didn't get to be a part of that government started to go elsewhere, either for land or to go trade overseas. interestingly, although the Norwegians and Swedes et al raided and colonized the northern parts of the British Isles, England was relatively safe from the Danes at the beginning of the Viking Age because of the heavy Frankish navy presence in the Channel. it was only when the Franks withdrew their military from the coast to deal with some civil wars that the Danes were able to really get going against England, which was basically defenseless without the Franks. (as a bonus, the Anglo-Saxon kings and nobles ousted by the Danes usually fled to the Frankish royal court to live the rest of their lives in exile.)

ironically, that bit of the northern coast of France that the Frankish forces eventually left? yeah, Charles the Simple gave that bit of land to some viking warlord named Hrólfr (Rollo, as he's known in English), who formed the Duchy of Normandy and... promptly allowed more Danish vikings to use the coast to stage raids on southern England. in the later part of the Early Middle Ages, when these viking raids on England increased in number and became more and more intense and destructive and everything really started spiraling out of control, the Anglo-Saxon king Athelred the Unready got desperate enough to pull two Pro Gamer Moves that would ultimately result in three or four different invasions of England during and after his lifetime: he married Emma of Normandy, and he ordered the deaths of every male Dane in England. the St. Brice's Day Massacre led to Cnut the Great invading England and seizing the throne, and the marriage to Emma of Normandy eventually led to William of Normandy making up a claim on the English throne, which then led to its own series of historical dominoes, including the England-France rivalry that lasted throughout the rest of the Middle Ages and the Modern Period until the defeat of Napoleon.

speaking of the Anglo-French rivalry: for most of the Modern Period until the rise of Germany, Denmark-Norway was often in the middle of the power struggle between England/Britain and France, at some points allied with the French and at others allied with the Brits, though overall more in the French sphere of influence than the Brits' just due to geography (ie Denmark could only ally with the British when the French felt like tolerating it). the Danes did successfully play the Brits and French against each other to gain some advantages, though unfortunately, the Brits and French were generally more inclined to just strongarm the Danes than to compete for influence. the Brits and French also always played some part in negotiating post-war treaties between Denmark and whoever the Danes were fighting, particularly when it was Sweden or Germany/Prussia, and of course occasionally Britain would join Denmark or Sweden if France was on the other side. this only really ended after the Napoleonic wars and especially after the Schleswig–Holstein wars as the balance of power shifted from France to Prussia/Germany. although Britain and Germany did vie somewhat for influence over Denmark, Denmark at this point was too weak and too close to Germany for Britain to make the effort.

nowadays under NATO, there's not really any tension that I'm aware of except that maybe the Danes were pretty upset about Brexit because it meant the EU lost its biggest trade-friendly member that could be counterweight France and Germany's protectionist policies.

tldr