Frederik Johan van Baer, Lord of Slangenburg (27 July 1645 – 15 December 1713) was a Dutch officer in the military service of the Dutch States Army. He served under William III of Orange in the Franco-Dutch War and Nine Years' War. He was to become a controversial figure for his role in the War of the Spanish Succession. While undisputetly a talented general, according to some the most talented of the Dutch generals, he possessed a very difficult character. Slangenburg was time and again at odds with his fellow generals, especially the Allied commander-in-chief, the Duke of Marlborough. The hero status he aquired as a result of his conduct in the Battle of Ekeren couldn't prevent his eventual dismissal during the 1705 campaign. Leading writer Thomas Lediard to remark that Slangenburg: lost by his tongue what he had gained by his sword.
Family
He was the son of Herman van Baer van Slangenburg (1610–1653) and Catharina van Voorst (1620–1678). In 1665 he married Dorothea Petronella van Steenbergen, who died the same year. Frederik never remarried.
Career
He was a professed Catholic, and therefore was denied a career in government. A career in the army was the obvious choice. Overcoming the challenges posed by his faith, he had a distinguished career in the Dutch Army, participating in the Franco-Dutch War, the Nine Years' War and the War of the Spanish Succession. At what age he entered military service is not known. The earliest known mention of Van Baer as a state officer dates from 1668, when he was already a captain of infantry. This makes it probable that he participated in the Second Anglo-Dutch War to.
Early on he already managed to make himself one of William of Orange's favourites. From the Rampjaar of 1672 onwards, promotions followed one another in rapid succession. On 27 October 1672, he was made a major in the first Regiment of Van Stirum and less than a year later he had already been promoted to lieutenant-colonel. In 1675 he was retroactively appointed colonel of one of the Dutch-Scottish regiments on the basis of bravery shown during the Battle of Seneffe. During several battles, he personally led his regiment into battle. On 11 August 1676, he suffered a severe injury to one of his femurs during the Siege of Maastricht and had to be carried off the battlefield. His brave and skilful performance at Trois Trous in Luxembourg brought promotion to brigadier a year later. In 1678 the Dutch and French signed the Treaty of Nijmegen, which ended the Franco-Dutch War. He became major general in 1683.
In 1688 war broke out again with France. Slangenburg didn't join William III during his invasion in England, but served with the Allied army in the Spanish Netherlands. In 1689 he would play a decisive role in the Battle of Walcourt. On 7 January 1690, however, he arrived in England to complain personally to William about his bad relations with the Prince of Waldeck, under whose command he had to serve. With Waldeck he had been in constant conflict. At the same time, he applied for the lieutenant-general position. When it became clear that William III would not give him his way in this, he threatened to resign and furiously announced that both Emperor Leopold and the Elector of Bavaria were vying for his favour. Slangenburg eventually effectively resigned from the States Army in 1690, but two years later, at William III's intercession, he was retroactively appointed lieutenant general of infantry.
War of the Spanish Succession
During the War of the Spanish Succession (1702-1713), Van Baer's military career culminated. He was among the commanders of the Dutch troops that came to fight the Franco-Spanish army in the Southern Netherlands under the allied supreme command of the Duke of Marlborough. Relations between the Dutch senior officers were extremely poor due to mutual rivalries and antipathies. At the same time, the cautious Dutch senior officers were suspicious of their English commander-in-chief. They blamed Marlborough, with troops largely financed by the Dutch Republic, for pursuing a risky offensive strategy which, in the event of a French breakthrough, posed a great danger to the defence of the Republic's land provinces (Slangenburg was from one of the land provinces). Slangeburg was involved in secret consultations in The Hague as early as 1702 of 'malcontents' from various regions who did not trust Marlborough's intentions and tactics.