u/DeRuyter67

To understand why the Dutch Republic invested so much but gained so little in the War of Spanish Succession (WSS), we have to understand the dynamic between the nations, and the dynamic between the staten of the Dutch Republic. We will start with the latter.

The Dutch Republic at the onset of the War

Since the ramjaar of 1672, the Dutch Republic had struggled in its identity: will it become a true Republic, or will it allow a strong Stadtholder lead it? William III had risen to the occasion when the Republic was at its weakest but Republican, anti-Orange, anti-Stadtholder sentiment was at its strongest, with Louis XIV of France choking it. Yet he was forced into an unsatisfactory peace in 1678 by the States-General that left Louis XIV too powerful, with few restraints.

Even as William III became Standtholder and eventually King of England, Scotland, and Ireland -- thereby becoming the Stadtholder-King -- this Republican, anti-Orangist sentiment continued. One outstanding agreement that the two parties had was that they needed to contain Louis XIV, and that Louis XIV cannot be trusted. This dictates compromises throughout.

Throughout the period between 1672 and the outbreak of WSS, the Republic had two key concerns, namely security in the southern Netherlands and in the open seas. When William III set up the Anglo-Dutch alliance, he was concerned with the containment of Louis XIV, and as the Dutch were the only ones who could reliably garrison the barrier fortresses in the southern Netherlands. Thus, William III set up the treaty whereby to save costs, the Dutch maintained the larger army while Britain maintained the larger navy.

When William III died without heir, all the pent-up anti-Orangist sentiment came to fore. Even though he had groomed Johan Willem Friso as successor, Holland regents refused to accept him as Standtholder. In many cities, factions of anti-Orangists returned to power. Zeeland stood with Holland and rejected Friso. There were riots in Gelderland.

This was the political situation when WWS broke out. Economically, the Dutch were on a downturn as well. As Philip V took the throne in Madrid, he transferred asiento contracts to French merchants, against the interest of the Dutch. The VOC shuttered its direct trade with Spain even as its trade with the French had been punished by high tariffs. Thus, removal of Philip V was a key goal for the regents of Holland. This was aligned with Austria, and Britain's Whigs.

Here we start to see a divergence of interests between factions in the Dutch Republic.

How the War went

No one nation of the Grand Alliance could stand up on its own against Louis XIV, yet they had divergent goals and conditions for peace. The Dutch Republic began the WSS with the largest army: 119,000 against Britain's 79,000. This was necessary, as France attacked its barrier fortresses. Yet it was apparent that its economic power had declined. Britain was providing the larger share of subsidies to their German allies. So this was a bad situation for the Dutch Republic, as its obligation was larger (due to its larger army) yet its financial resources was stretched further (due to economic decline, and downturn in trade).

The divergent goals and conditions for peace forced the war to continue beyond the aspirations of certain members of the alliance, yet they cannot back out for fear of being isolated. For the Dutch, this was worse as even internally, they were divided. A secret agreement dictated that Dutch troops cannot be commanded without consent of Dutch generals and States-Generals' deputies; even as Marlborough is theoretically the overall commander.

Even as the Dutch had to stretch themselves through a severe slump in 1704, the Allies won major engagements in the Low Countries as they avoided sieges. By 1706, the situation looked bright for the Dutch. Unfortunately, Philip V was winning in Spain itself, not only militarily but also politically. As a result of this, the goal of removing Philip V became an unattainable goal that stretched war beyond what the Dutch had set itself to accomplish. If they were to take up Louis XIV's offer for peace and favorable trade, they would either be isolated, or incur the wrath of Britain and Austria, or both. Further, there was also Louis XIV's track record of taking advantage of the Dutch. In spite of overtures, the States-General rebuffed Louis XIV.

How the War was settled

By 1710, Louis was desperate and even offered that he forfeit his support of Philip V. However, this leaves out the issue of how to actually remove Philip V, who had proven popular with many factions in Spain. The Dutch and the Austrians remain committed to the war, with the ultimate aim of removing Philip V by force. However, all parties were becoming exhausted and thus murmurs of peace began to be heard.

Negotiations had been initiated in Utrecht in 1712 to settle for peace. However, in this time period anti-government sentiment in Britain came to fore, and the Tories came to power. This brought about a major change in requirements for peace: Britain would now accept Philip V as king of Spain, in return for significant trade advantages and control of Gibraltar and Minorca.

The rest of the Allies felt betrayed, and Austria attempted to forge a new smaller alliance with the Dutch to resume the war; however these two were not strong enough to counter Louis XIV and Philip V. Thus, the Austria and the Dutch were forced to accept a bad deal.

TL;DR

The Dutch were disunited; the allies even worse; a change in political climate meant Britain forced a bad deal on its allies.