A few days later, after Bismarck's incitement and urging, Austria and Prussia reached an agreement.
The Austrian army would continue, together with the Prussian army, to attack the Danes, unless the Danish government agreed to the complete independence of the two duchies.
Of course, Denmark could not possibly agree; losing Schleswig meant losing more than thirty percent of Danish territory, and nationalist factions at home would certainly brand the cabinet as traitors.
Compared to surrendering without a fight, defeat in battle would arouse more sympathy among the Danish people—not because the government failed, but because the Germans were too despicable.
The Danish government rejected the conditions set by the German states, so the Allied war machine once again roared into motion.
On March 8, upon receiving orders from home, the Austrian Empire's army was the first to launch the campaign, and won the Battle of Weiler.
On March 15, the Danish navy announced the blockade of the Prussian coast. The navy entered the war, and the newly established Prussian navy responded.
Fierce exchanges began between the two naval fleets in the waters of Yasmond. At that time, the Prussian navy had only recently been established, whereas Denmark was a traditional naval power in Northern Europe. The outcome of their clash was self-evident. Two days later, Denmark achieved a tactical victory in the Battle of Yasmond.
The feeble Prussian navy was no match for the Danes; Denmark firmly held control of the sea. However, the Prussian navy preserved its surviving forces, avoiding total annihilation.
On the same day, the Prussian army launched an assault against Danish positions at the new Di Bo'er lines, first deploying artillery for a massive bombardment, then advancing under cover of the barrage.
Facing the ferocious Prussian troops, the new Danish commander naturally dared not repeat the mistake of General Mesa; this time, he chose not to withdraw from the battlefield. Relying on stubborn resolve, the Danes repelled Prussian probing attacks several times in one day.
Yet, this clash was merely a prelude; the Prussian army's true offensive was still being assembled.
A month later, on April 18, the Battle of Di Bo'er erupted. After dozens of hours of preparatory bombardment, Prussia launched its full-scale assault: several hundred cannons simultaneously bombarded the Di Bo'er positions, while, despite the firepower from Herolff anchored off Denmark's coastline, they pressed forward with a fierce attack.
As Denmark's flagship, Herolff was clearly unable to halt the Prussian land advance, and could only temporarily slow the army's progress.
Under the blanket strikes of artillery, the Danes could only cower in their fortifications, while the Prussians seized the moment, leveraging their manpower advantage to advance toward Di Bo'er.
Gradually, the advance units at the forefront reached the edges of the Di Bo'er positions.
Under the powerful Allied cannon fire, Di Bo'er lines were all but on the brink of collapse; many makeshift fortifications had been reduced to ruins under the bombardment.
The Prussian troops who reached Di Bo'er used these ruins to penetrate deep into the Danish defensive lines.
Observing that the situation was lost, the Danish chief commander could only order the troops to abandon Di Bo'er, leaving behind the Eighth Danish Army Brigade as rearguard.
The Eighth Danish Army Brigade fought tenaciously to cover the main force's retreat.
However, losses were especially severe; the brigade was nearly destroyed by the Prussian onslaught, with casualties exceeding a third, but it accomplished its mission superbly—covering the withdrawal of Denmark's main force.
Following defeat at Di Bo'er, Denmark's military, hampered by insufficient manpower, was forced to abandon operations to reclaim Fredericia, which had already fallen to Austrian troops.
Through a series of Allied battles, Danish territory on the Jutland Peninsula (including Schleswig) was lost nearly by half. Even the hope for Danish victory—the faintest flame—had been snuffed out by the Allies.
Meanwhile, Denmark's successive defeats prompted the United Kingdom government to intervene, for maintaining the continental balance was a British bottom line: the British cannot allow enormous changes among Europe's nations.
The British government had already issued a stern warning to Prussia, and Prussia verbally agreed to a temporary ceasefire on April 12.
But Bismarck postponed this plan to April 25, during which time Prussia took control of the entire Di Bo'er area.
After gaining support from Russia, France, and Sweden, the British proposed intervention in the Jutland Peninsula conflict, asserting the entire Schleswig issue should be resolved by a decision of the European nations.
Austria and Prussia, who had already secretly agreed, stated that so long as the 1852 agreement was not the basis for resolution, and the duchies were linked to Denmark only through personal relationships, they would accept a settlement.
The conference was convened in London on April 25, chaired by Viscount Palmston, the British delegate.
The United Kingdom accused Prussia and Austria of acts of war that threatened peace in Europe.
But the German side's representatives merely replied that such problems were inevitably fraught with disorder.
At the same time, Count Boyst, representing the German Confederation, demanded recognition of Augustenburg's sovereignty over the duchies.
While Austria tended to favor a plan similar to the 1852 agreement, Prussia had already shown ambition to obtain the duchies.
For the Kingdom of Prussia to realize this ambition, it must first secure complete independence for the Duchy of Schleswig.
Thus, the Prussian delegates insisted upon total independence of Schleswig from Denmark.
This placed Austria in a dilemma: if it opposed, it might lose all influence over the German region; if it did not, Prussia's power would surely rise.
Weighing the pros and cons, Austria felt influence in the German region was more vital; after all, unifying all of Germany was also a goal of the Austrian Empire.
Thus, Austria, with reluctance and reservations, supported Prussia's proposition for Schleswig's full political independence, but insisted on joint oversight by institutions—which left the next steps undecided.
To reassure the United Kingdom, France, and the Russian Empire, Prussia's representatives declared that Prussia would not seek lands beyond Schleswig and Holstein.
This satisfied the demand of other great powers that the Danish Straits—providing passage to the Baltic Sea—not be controlled by other major nations.
Sweden's delegates made no statement. Historically Denmark was Sweden's rival; if Prussia and Austria could weaken Denmark, Sweden would welcome it.
Of course, this depended on the German Alliance Army not swallowing the entire Jutland Peninsula—otherwise, Sweden would face geographic dangers even worse than those caused by Denmark.
Clearly, neither Prussia nor Austria considered Denmark's concerns, and Britain and others had already reached tacit agreement on Prussia's terms. The Danish government rejected the proposal.
This London conference did not fundamentally solve the Jutland Peninsula problem, but temporarily paused the attacks from Prussia and Austria.
Taking advantage of the conference timeframe, Denmark completed its final mobilization. Most of Denmark's attempts on the Jutland Peninsula had ended in failure.
Troops withdrew to Als Island to continue resistance. In June, Prussian troops began to gather opposite Als Island. The Second Schleswig War was about to enter a new phase.