March across the Belts. The Swedish troops cross the ice to Zealand, 1658: painting by Johan Philip Lemke (1631–1711)
Swedish military engineer and general. Dahlberg was an innovative engineer in the mold of Vauban and Coehoorn, to the point that he is sometimes called the “Swedish Vauban.” Like all top military engineers of the era, he both built fortifications and helped attack and defend them. Among his important sieges were Copenhagen and Kronborg. He also carried out two successful defenses of Riga. In 1658 he conducted a Swedish army over several frozen rivers en route to Denmark. His most famous feat was to cross the frozen Great and Little Belts of the Denmark Strait. This enabled an attack on Copenhagen, before which he famously entered the city alone and explored its defenses for several days as a guest of Danish officers he knew. With remarkable foolishness, they gave him a tour of the city’s defensive works. Dahlberg also commanded Swedish engineers during several wars in Poland, the Scanian War (1674-1679), and the first years of the Great Northern War (1700-1721). His influence was perpetuated through his life example, skill at map-making, fortresses he designed, and widely published writings on military architecture.
After decades of failed, costly, and aggressive war leading to humiliating defeat under Christian IV (1588-1648), Danes were left without a taste for war at the mid-17th-century mark. This mood placed severe restraints on Fredrik III when he succeeded his father in 1648 at the close of the Thirty Years’ War (1618-1648). Denmark had been excluded from talks leading to the Peace of Westphalia, as a result of which it lost Bremen to Sweden and Swedish ships no longer were forced to pay Sound Tolls. The Rigsdag would not vote funds to give the new king an Army large enough to tempt him to make aggressive war, in the process also ensuring that he did not have forces capable of national defense. Even so, when Swedish fortunes under Karl X looked to be at ebb tide, Fredrik declared war on Sweden. He thereby recklessly took a wholly unprepared Denmark into the Second Northern War (1655-1660) against a battle-tested foe whose state was organized for war. This proved to be a catastrophe. Guided by Count Dahlberg, Karl made a spectacular crossing of the frozen Belts with 5,000 Swedish troops, appearing suddenly in the suburbs of Copenhagen and compelling Fredrik to sign the Treaty of Roskilde (February 26/March 8, 1658). Karl then returned in August and besieged Copenhagen. Only aid from the United Provinces, and later from Brandenburg and Austria, saved the Danish capital from ruin.
In 1660 Denmark experienced what amounted to a constitutional coup d’état. Facing noble opposition to taxation, the non-noble Estates introduced a fundamental restructuring of the elective monarchy and state. In this move against the entrenched nobility they were supported by Fredrik III. Under threat of martial law in Copenhagen, the Rigsdag crumbled (October 23/November 2, 1660), voting to make the monarchy hereditary and to abolish noble privilege. The revolution was confirmed the following January. In less than a dozen years, and in face of several severe military defeats brought about primarily by reckless monarchs, the Danes nevertheless shifted from radical limitation of royal power to the new-style “absolute and hereditary monarchy.” This began a process of integrating the old noble elite of birth with a new, non-class-based elite of national service that would continue into the mid-19th century.
The Danish 1660s were consumed by a search for anti-Swedish allies and formation of a series of alliances that bore little fruit, and most of that bitter: with England in 1661, France in 1663, and the United Provinces in 1666. In September 1672, Denmark joined several small north German states, Leopold I of Austria, and Friedrich-Wilhelm of Brandenburg in a defensive alliance. The next year Denmark signed a naval alliance with the United Provinces, which agreed to subsidize a Danish fleet of 20 sail and an army of 12,000 men. This set the stage for the Scanian War (1674-1679), during which the Danes were once again highly aggressive, invading Scania and seeking its annexation. The young Swedish king Karl XI conducted a highly spirited and effective defense against the Danish invaders. The Danes lost at Halmstadt (a. k. a. “Fyllebro”) in August 1676 and suffered through an astoundingly bloody fight at Lund that December, proportionately the bloodiest battle in military history, with 50% of all participants killed. In 1677 the Danes twice tried, but failed to capture Helsingborg. They lost again at Malmö (July 5/15, 1678), and yet again at Landskröna (July 14, 1678). The Danes proved unable to advance beyond their holdings of Helsingborg and Landskröna, despite significant numerical advantages over the defending Swedes in cavalry, infantry, and artillery. The war also brought France against Denmark, in defense of Louis XIV’s Swedish alliance. The French penetrated Oldenburg, leading the Danes to quickly agree to the Peace of Fontainebleau (August 23/September 2, 1679). That ended the war between Denmark and France by forcing the Danes to promise to restore all their conquests to Sweden in exchange for a paltry indemnity to be paid to Denmark. The Peace of Lund (September 16/26, 1679) formally ended the war between Denmark and Sweden on the terms of Fontainebleau, and with confirmation that Swedish shipping remained exempt from paying the Sound Tolls.
Denmark remained unreconciled to the loss of Scania and the Swedish exemption from the Sound Tolls. With the Maritime Powers and Brandenburg neutral at best, and far more concerned with the threat from France, Fredrik IV (1671-1730) was forced to seek allies in the east for any war he hoped to wage against Sweden. He found a willing partner in Augustus II of Poland and, in 1699, Peter I of Russia. The three monarchs framed a secret alliance declaring a joint intention to wage a war of aggression leading to partition of the Swedish empire, all three hoping to take advantage of the passing of the more formidable Karl XI and the youthful inexperience of the new Swedish king, Karl XII. That proved to be a foolish wager, as the boy-king of Sweden swiftly emerged as a formidable opponent of all three attackers during the first half of the Great Northern War (1700-1721). Denmark paid first. Sweden quickly knocked Denmark out of the war with a bold amphibious operation: the Swedish fleet navigated the “Flinterend,” a dangerous passage between Sweden and Sjælland (or Zealand), to enable landing an army near Copenhagen on July 13-14/July 25-August 4, 1700. The frightened Danish king agreed to exit the aggressive alliance with Poland and Russia and left the war upon signing the Peace of Travendal (August 7/18, 1700). After Karl overreached by invading Russia, only to suffer disaster at Poltava (June 27/July 8, 1709), Denmark sought to take advantage by pouncing yet again on Scania. The Danes landed a large amphibious force there, while Peter personally opened a new siege of Riga. However, the Danes were soundly defeated at Hälsingborg (February 28/March 10, 1710), even in Karl’s prolonged absence at the Sublime Porte. That fight finally decided the issue of Sweden’s permanent possession of Scania. More fighting, the premature death of Karl XII, and Russia’s decisive victory over Sweden opened the door for Denmark to seek gains at the edges of the crumbling Swedish empire. Sweden agreed to the Peace of Frederiksborg (June 14, 1720) with Denmark (which signed on July 8th), accepting the loss of some territory and agreeing to pay the Sound Tolls after a hiatus of 70 years. Yet, the treaty was actually something of a defeat for the Danes, who lost Wismar and Rügen and gained, after ten years of war, only minor territory in Gottorpian Schleswig and a small indemnity of just 600,000 crowns.