Why did the Spanish succession become the main goal of Leopold I’s foreign policy?

For Emperor Leopold I, the Spanish succession became the central goal of his foreign policy due to his commitment to the unity and prestige of the House of Habsburg. He viewed the two branches of the dynasty—the imperial line and the Spanish line—as parts of a single, indivisible entail.1

Leopold’s pursuit of the Spanish throne was driven by several key factors:

• Dynastic Claims: Leopold held a legitimate claim to the Spanish inheritance through his marriage to Margarita Teresa, the daughter of Philip IV of Spain and sister of the childless Charles II. He further strengthened this position by persuading his daughter, Maria Antonia, to bestow her own succession rights upon him and his sons.21
• Geopolitical Strategy: Leopold sought to prevent the Bourbon dynasty of France from acquiring the vast Spanish holdings, which would have significantly shifted the European balance of power in favor of his rival, Louis XIV.23
• Dynastic Power: Leopold no longer prioritized the empire as his sole responsibility; instead, he elevated the power and prestige of the Habsburg lands and dynasty as his primary objective.1

When Charles II died in 1700, leaving the throne to a Bourbon prince, Leopold considered it a necessity to defend the Spanish heritage by force of arms, leading to the War of the Spanish Succession.13