The Danish War started with the planned three-pronged attack which involved a) Christian IV marching into north-west Germany b) Christian of Brunswick marching into the Rhineland c) Mansfeld would fight with Bethlan Gabor in Bohemia.
However, the coalition had one weak line in it before it even started campaigning - Christian IV of Denmark.
Christian was a ruler of land in Holstein and as such was a German prince in his own right. His interest lay not in Bohemia or Bavaria but in gaining control of Lower Saxony and furthering his influence in that area. He was also after the bishoprics of Bremen, Verden, Minden and Halberstadt. For commercial and strategic reasons he also wanted to control the valuable Hansa towns of Hamburg and Lubeck. If Christian could gain control of all of these, then Denmark could monopolise the lucrative Baltic trade.
Christian also found foreign help from the coalition lacking in material kind. The Dutch and English only offered moral support while the Danish king found it very difficult to co-ordinate a military policy with Brunswick and Mansfeld.
How did Ferdinand react to the Coalition’s threat ? As early as 1624, Ferdinand had appointed a military leader who was directly answerable to the emperor. This man was Albert on Waldstein though he is better known as Wallenstein. Tilly was head of the Catholic League which was answerable to Maximillian of Bavaria. If Maximillian decided to pull out of the war now that he was an Elector twice over, Ferdinand could find himself without a known military leader.
Wallenstein was an astute choice. In April 1625, he was created Generlissimo of all the Imperial troops. After recruiting 24,000 troops to fight for the emperor, he was made Duke of Friedland in June 1625. Wallenstein was a complex man but a ruthless tactician. He and Tilly made for a formidable combination and in the Danish War the three-pronged attack of the coalition stuttered to a halt.
In April 1626, Mansfeld was defeated by Wallenstein at the Battle of Dessau Bridge. In April of the same year, Christian was heavily defeated by Tilly at the Battle of Lutter.
In late 1627, Christian was driven back into Denmark. Holstein, Schleswig and Jutland were occupied by Tilly.
After Dessau Bridge, Mansfeld tried to link up with Bethlan Gabor but Gabor had already come to terms with Ferdinand. Mansfeld was left wandering in Balkans with his army. His unpaid troops deserted him and Mansfeld himself died in Sarajevo in November 1626.
In 1628, Wallenstein occupied Mecklenburg. He was made Duke of Mecklenburg and Ferdinand appointed him "General of the whole Imperial Fleet and Lord of the Atlantic and Baltic". Wismar and Rostock, important and lucrative Baltic ports, fell under Imperial control.
The fall of these two ports gave Olivares the opportunity to put into effect his almirantazgo policy. The plan was simple. By uniting the trading towns of Flanders and the Hansa, Habsburg forces could wrest control of the carrying trade from the Baltic to the ports of Flanders. Dutch sea borne trade would be strangled as the Habsburgs would control movement in the seas off north Europe. This would be a massive boost to Spain’s economy as once again she had gone bankrupt in 1627. It would also undermine the ability of the Dutch to defend themselves as investment in their military would dry up and they would not have the financial clout to pay for mercenaries or buy in foreign troops from the likes of Sweden, for example.
Olivares wanted his plan organised by an Inspectorate for Commerce (Almirantazgo de los paises septentrionales). On paper his plan was good. By bankrupting the Dutch and controlling mercantile trade in the Baltic and the north coast of western Europe, he would re-establish Spain’s economy and elevate the status of the Habsburgs once again throughout Europe. But it had one flaw - the plan depended on the co-operation of Wallenstein and he was not in favour of the plan simply because it took power away from him in the Baltic.
Wallenstein saw the Baltic as his ‘territory’ and he did not want Spanish interference in the region. It was one of Europe’s most lucrative regions and any money made there, Wallenstein wanted to keep. In support of him were the trading towns of Danzig and Lubeck. Wallenstein was also concerned that the building of an Imperial navy to protect Hansa trade, might provoke a response from Sweden. He feared that Gustavus might invade northern Germany to assert his authority in the area. Wallenstein saw north Germany as his and he did not want the region devastated by war as he would lose a great deal of money if this occurred.
This example shows the difficult position Ferdinand was in. The Spanish Habsburg’s via Olivares had what was potentially an excellent plan to re-assert Habsburg power throughout Europe. But the Austrian Habsburg’s , under Ferdinand, seemed to have lost control of their highly successful general Wallenstein who had begun to see himself as a law unto himself.
In July 1628, Wallenstein attacked Stralsund in Pomerania. His claim was that it would extend the emperor’s power - but it would also greatly increase his own as Stralsund was a wealthy city. The attempt failed as Stralsund called on Denmark and Sweden to aid it. Both did, and Wallenstein had to withdraw from besieging Stralsund.
Christian IV - believing that Wallenstein’s forces were weakened - followed up this success by landing a force in Pomerania. In fact, Wallenstein’s force was still very strong and Christian’s army was heavily defeated at Wolgast in September 1628.
However, Wallenstein realised that such a victory might provoke a response by Gustavus of Sweden and he persuaded Ferdinand to agree to generous peace terms with Christian despite the fact that Denmark was incapable of continuing a military campaign.
In the Treaty of Lubeck (June 1629), Denmark was allowed to keep her possessions including the valuable state of Holstein; Christian had to give up his claims on the north German bishoprics and his leadership of the Lower Saxon Circle. He also had to formally withdraw from the war.