|Make Talk, Not War|
Violence, shooting and other sundry unpleasantries were sometimes not necessary to take an artillery fort.
Talk was preferred. It cost far less than having an army make a siege - even if the talk was sweetened with bribery.
The Spanish especially preferred to suborn a fort's governor or garrison commander before firing their cannon. In the Netherlands, the English yielded the fort at Grave in 1586 to the Army of Flanders after silver crossed their collective palm. Three years later, frustrated at remaining unpaid by their side, other English defenders opened the gates of Geertruidenberg to the Spanish. The Spanish garrison at Fort St. Andries in 1600 succumbed to a Dutch bribe after the siege had begun. Other similar incidences happened across Europe during this period.
Between 1574 and 1589, some Dutch towns capitulated to the Duke of Parma's Army of Flanders simply because their defenders beheld a strong, combat-tested army before them and they considered about how feeble were their old, medieval walls and half-built fortifications. One of Parma's strategies was to coerce small towns in an area to surrender, thereby isolating any fort there. Next, communications to that fort were cut off while the Army of Flanders constructed its own fortifications. By 1589, the Spanish were back in control of 75% of the Lowlands. But then Phillip II distracted Parma by insisting he meddle in the affairs of France - and there was also that inconvenience of the Spanish fleet being devasted in 1588. The opportunity to strike back and regain lost ground was not lost on Maurits Van Nassau and his Dutch.
Losing a major field battle could affect the fortunes of garrisons and fortifications throughout an entire region. The Swedes and their Protestant allies abandoned much of southwest Germany after losing the Battle of Nordlingen in 1634 (in an attempt to break the Imperialist siege of that town). Following the royalist loss at Naseby in 1645, most of that side's garrisons in the English Midlands threw in the towel. The exception was the Netherlands in which one artillery fort was so close to another that a victorious army advancing bumped all too soon into an enemy's artillery fort.
A change of heart of a high personage could do more damage than an army. Count Henrik van den Bergh (1573-1638), nephew of William of Orange, commanded the Spanish Army of Flanders in Germany from 1624 to1628, then in the Netherlands in 1629. But in 1632 the Count turned against his employer, the Spanish Empire, led a revolt and invited non-Spanish soldiers of the Army of Flanders to free themselves "from Spanish slavery." His urgings persuaded the garrisons at Venlo, Roermond and Maastricht to open their gates to the Dutch, thereby nearly cutting off the Spanish Netherlands from Catholic forces in Germany (and the result may be seen in maps today: a protrusion of the Netherlands border in the southeast).