Why did Germany not become a major colonizer of overseas countries, like England and France, and even Belgium?
First, there was hardly such thing as "German monarchs": before Bismarck Germany was fractured into a bunch of small states, each with its own monarch. True, they were formally united into "Holy Roman Empire of German People", but, as Voltaire pointed out, "Holy Roman Empire is neither Holy nor Roman nor Empire". And when Bismarck finally united Germany it was too late for colonization: the World was pretty much already divided up by other European powers. Not that Germany didn't try: its ambition to redraw the World is sometimes cited as one of the causes it was so eager to launch WWI.
Second, Germany was mostly a continental country, not land-locked of course, but further from the routes to the usual colonization lands. Most of the German fleets were involved in Baltic Sea trading, not across-the-ocean ones. Not surprisingly, early German attempts for colonization were directed Eastward along Baltic Sea: one can say that Hanseatic League expansion into Livonia and Estonia was an attempt to colonize North-East Europe.
- Colonization: (of a country or its citizens) send a group of settlers to (a place) and establish political control over it.
I would argue that in fact Brandenburg-Prussia engaged very successfully in the colonization of Western Pomerania (1653); Magdeburg (1680); Eastern Pomerania (1720); Silesia (1740); Pomerelia & West Prussia(1772-1793); Schleswig-Holstein(1864); Hanover, Hesse, Nassau & Frankfurt(1866); and finally Bavaria, Lower & Upper Saxony, & Alsace-Lorraine (1870) to establish the German Empire.
While this Empire was not an overseas empire like the Dutch, British and French, it was still very much an Empire; ruled by Prussians for Prussians. In the early 1900's the German Empire was the pre-eminent leader in physical science research, and was surpassed economically only by the United States and the British Empire. Brandenburg Prussia truly had arisen to a world power from very humble beginnings in 1600.
It is worth noting that:
- The Brandenburg Gold Coast was sold to the Netherlands in 1720 (for 7200 ducats);
- Arguin was held by Brandenburg 1685-1721 until taken over by France;
- Saint Thomas was held by the Brandenburgisch-Africanische Compagnie from 1685-1720;
- German East Africa (Tanganyika, Ruanda-Urundi, Wituland), German South-West Africa (Namibia), and German West Africa (Kamerun & Togoland) were held from 1884 until the First World War.
- The German Empire held the colonies of German New Guinea and German Samoa in the Pacific until 1914.
Germany was't even a unified country until 1871, which is to say that until that time, it had more to worry about its own internal problems, than with colonies.
By 1871, the Monroe Doctrine had made the Americans off-limits, and most of South and East Asia (India, Indochina, and modern Indonesia) was spoken for by the English, French, and Dutch respectively.
That left mainly Africa, where England already had a head start in Egypt, South Africa, Gold Coast (Ghana) and Nigeria, and France in what became "French West Africa." Germany, Belgium, and Italy were left with the less accessible, less desirable parts of the continent. Germany finally got modern Tanzania and Namibia, Belgium (Congo), and Italy Libya and Ethiopia (the latter only in 1935).
Germany also tried to expand in Eastern and Southern Europe. It created the "Berlin to Baghdad" railroad around the time of World War I, and tried to help allies Austria-Hungary and Turkey expand in the Balkans and Middle East, while conquering Poland and Ukraine from Russia in World War I.
When Hitler formally renounced "colonies" in 1935, he meant "overseas" colonies, not the "close to home" variety in Eastern Europe and the Soviet Union. Unlike e.g. Britain, Germany didn't have enough of a navy to support overseas colonies, but had an army that was more than willing to annex adjacent territories.