His Kriegsbuch contained all the military knowledge of his time, but also many new ideas, which made an essential contribution to the reform of the Dutch States Army by his cousin Maurice.

The men were favourably inclined towards this measure, because they saw for themselves how they could gain a huge amount of time by continuous practice in handling weapons and thus had a great advantage over their opponents.

In Nassau, and especially in the Siegerland where it was introduced first, there was never any protest against the general conscription, because the population considered the Counts' struggle for the freedom of the Netherlands as their own.

A new type of mortar invented by John, together with the corresponding incendiary bullets, both of which he had made cast in Siegen, was tested at the Siege of Groenlo in 1597 and had a devastating effect.

Together they form a Kriegsbuch that reflects all military knowledge of the time, but above all contains a wealth of completely new ideas, from the art of large fortifications to the most advantageous arrangement of a 'secret chamber'.

[1]In the great theatre of operations of the Counter-Reformation, King Sigismund III, the Catholic Vasa, had united Poland and Sweden in his hand.

Charles immediately offered John the supreme command,[note 4] which he accepted "trotz der geringen Lusten" ("despite the low desire"), but only for a period of three months, because the Swedish army was in a more than poor condition.

The foot soldiers, for instance, were so miserably armed that John devised and immediately ordered the production of spiked carts, which were pushed in front of the infantry and proved to be a great protection against the attacking cavalry.

[6] After three months, during which John had won several skirmishes and captured much material from the Poles, but had not been able to bring the Siege of Riga to a successful conclusion, Charles begged him to stay in Livonia and remain in command.

Charles provided a Swedish naval ship for the journey to Lübeck, which had to remain on Bornholm for a long time due to violent storms.

[1] The extent of John's ambitious political plans and the power of a Protestant Union, as he imagined it, is best shown by the fact that in 1598 he seriously wanted to promote the idea of electing his cousin Maurice of Nassau as German king.

Their common goal was to win over Elector Joachim Frederick of Brandenburg to the Protestant cause, and to this end they wanted to help him acquire the disputed duchy of Jülich-Cleves-Berg.

[8] In September 1610, as an envoy of the Protestant Imperial Estates of the realm, John negotiated with the leader of the Catholic League, Duke Maximilian I of Bavaria, where they reached a mutually satisfactory agreement.

[7] When the young Elector Palatine Frederick V was urged by the Protestant Imperial Estates to accept the Bohemian crown, he did so after extensive consultation with John and Christian I of Anhalt-Bernburg.

He was also commissioned to draw up plans to strengthen the Rhine from Bonn to Rheinberg, to modernise the fortress of Düsseldorf and to design a system of fortifications for the Ruhr, Ems and Lippe rivers.

In a letter of 8 December 1608 he even considered the death of his son Adolf as a punishment from God and he exhorted the two others, who with "einem ärgerlichen Leben mit Verschwendung fast allem, was ich in der Welt habe, durch Ehebrechen und Hurerei, Plünderung und Beraubung armer, unschuldiger Leute hoch und niederen Standen" ("an annoying life of squandering almost everything I have in the world, through adultery and fornication, plundering and robbing poor, innocent people of high and low rank") ruined the county of Nassau-Siegen, to lead a different, better life, worthy of the name Nassau.

Yet it took the most urgent appeals of his brothers to persuade him at last to abandon his friend's cause and return to Siegen, where he, martial and capable as he was, diligently devoted himself to all preparations for the protection of town and country.

[7] John's idea to give the Protestant cause good leaders for a people's army, was the reason for the Kriegsschule, founded in Siegen in 1616, probably the world's first military academy.

But despite the fact that he was so indebted by supporting the Dutch Revolt, that for some time he considered giving up his residence in Siegen and going to live with his brother William Louis, he nevertheless founded the school.

The other descendant of John was Friedrich Wilhelm von Steuben, the organiser of the Continental Army and an important aide to George Washington.

[8] When John received the County of Nassau-Siegen in 1607, he decided that such a small country (it had about 9,000 inhabitants and yielded an annual revenue of about 13,000 guilders) should not be divided up again.

[15] He therefore repeatedly turned to his cousin Maurice of Orange to obtain from him an assurance of assistance in the event that his son would not keep his word and would use force in Siegerland with the help of Spanish or imperial troops.

[24] Only once he was convinced that his son was under the influence of the Jesuits and that the possibility of a Catholic area within the Nassau lands was a danger to the Protestant inhabitants, did he get persuaded to make a new will.

[15] On 3 July 1621 he drew up a third will, in which he laid down something that he had always considered to be utterly nonsensical, namely to divide the small county of Nassau-Siegen, which was barely able to support one lord, into three parts.

He had taken the precaution of obtaining a further imperial decree on 20 November 1623 against Countess Dowager Margaret and her sons, in which the Emperor strictly forbade impeding John's assumption of government, his taking possession of the land and his inauguration.

However, for a short period (1632–1635) this situation underwent a temporary change: during the Thirty Years' War, his brothers, who were fighting on the Protestant side, rebelled against John the Younger.

[26] Count Louis Henry of Nassau-Dillenburg entered the service of King Gustavus II Adolphus of Sweden on 1 December 1631, who had landed in Germany on 24 June 1630 to intervene in favour of the Protestants in the Thirty Years' War.

[34] Countess Dowager Margaret, through the mediation of Louis Henry, turned to Gustavus Adolphus and asked for help against the machinations of her stepson John the Younger.

Consequently, on 14 February 1632 the Swedish king sent an order from Frankfurt to Louis Henry to provide military support for his first cousin John Maurice.

[37] On 22 January 1645, after his return from Brazil, the latter, with his brothers George Frederick and Henry and an 80-man entourage, had forcibly occupied Siegen Castle and on 15 February had received the renewed homage from the citizens, albeit this time only for two thirds of the county.