The Low Countries
Caught again between two European Great Powers, and both relying on their neutrality, were Belgium thought it was protected with the treaty of 1839.
Although the war of 1870 showed this neutrality could be difficult to enforce. Lessons were learnt form this war and large investments were made by both countries how . First in fortification and later in a restructure of the armies. However the latter this took considerable time and by the 20th century the urge to made this inovations faded away. The Netherlands was a bit earlier in this army reforms but Belgian politicians were too contemplated about this. Also the two small countries did not co-operate with each other. A overture by the Netherlands in 1912 was never answered by Belgium and when the June crises of 1914 spiraled out of control during the next month Belgium asked for military cooperation. This time the Netherlands rejected this since military investigations predicted that the German war machine might pass the Netherlands but not Belgium.
Fortunately for Belgium this assessment of their Northern neighbors was incorrect. Never the less the Belgian mobilization was not really smooth and highlighted the lack or too late investments. More crucial was the multitude of war plans and the internal conflicts within the army staff. The latter was the main reason King Albert took in person the command of the Belgian army.
Even the war seemed to be limited just South of the Belgian border the imminent treat that one of the belligerents would out flank the other via Belgian or Dutch territory remained.
This threat forced the two small neutral countries to cooperation. First a military cooperation and later an, although temporary, custom union. The military cooperation was initially limited to an exchange of military attachés in the general staffs. In 1916, after nearly a year of long leave for most conscripts, the scare of invasion become suddenly imminent. The invasion scare came more from France, both Belgian and Dutch high command had clear information that France could launce an invasion in to Belgium and possible Southern Netherlands a desperate attempt to out flank the Germans.
In order to deal with this threat nearly entire Belgian army would be concentrate to the Franco-Belgian and the fortification line along the river Meuse and Sambre. the The Dutch army would hold the Meuse line North of Liege, with the 3rd and 4th divisions of the filed army, while the 1st division would be relocated between Antwerp and Malines as a reserve for the Southern front or the Eastern front.
The cooperation between the two nations was the combined effort of the monarchs of both nations. King Albert of Belgium and Queen Wilhelmina of the Netherlands.
King Albert could assured more influence since after he took command of the armed forces he took more and more power, some critics wrote he acted almost as an absolute monarch. For Queen Wilhelmina it was more precarious but never the less due to their effort not only close military cooperation but also economic cooperation was established.
King Albert took the opportunity during this war year not only to speed the modernization of the armed forces but also to implement several reforms, especially to the emancipation of Flanders.
Even both countries had to maintain relative large armies during this period, the economy was booming. The ports of Rotterdam, Antwerp and others were open and not hampered by any naval blockade. The exports of both countries to Germany and France exploded, as far as it did not endanger the neutrality too much. In matter of fact the industry had a severe labor shortage, inflicted by the large number of conscripted men and the exploded demand.
The cooperation in both military and economic turned out to be very well and despite this cooperation was intended to be temporary, the international situation dictated differently.
After the Berlin peace conferences the power block which emerged around Germany was intimidating. In order to form some sort of counter force, even limited, and in case of any future conflict between Great Powers, Belgium and the Netherlands decided to extend their cooperation.
In 1920 the Union of Brussels was signed. This was done in a grand ceremony at the Royal Palace of Brussels by King Albert and Queen Wilhelmina. The Union of Brussels referred in a distance tot he Union of Brussels of 1577.
The union comprised a military alliance, safe guarding their neutrality, and a custom union, a Schelde river treaty and over time would be extended with more agreements.