The whole Habsburg claim was fought out in the War on the Spanish succession and has been 'settled' with the Treaty of Utrecht in 1713. In 1700 Don Carlos de Habsburgo y Borbón, King of Spain, of Naples, of Sicily, of Sardinia, Duke of Luxembourg and Lord of the Netherlands died. His two marriages with Marie-Louise d'Orléans and Maria-Anna von Bayern were without issue.
The strongest claim on the throne of Spain had Don Carlos II's nephew Louis de Bourbon (1661-1711),
Dauphin de France, son of Louis XIV de Bourbon, King of France and of María Teresia de Habsburgo y Borbón (sister of Don Carlos II). Because Louis ("
le Grand Dauphin"), and his eldest son Louis ("
le Petit Dauphin") had to remain available for the succession to the throne of France, he transferred his rights to his second eldest son Philippe de Bourbon,
Duc d'Anjou.
----
Don Carlos II of Habsburg, King of Spain died in 1700. No issue. Note that the succession in Spain was semi-salic: sons had preference over daughters in the same degree of consanguity, which means that the succession could be transferred to females by lack of male heirs.
His brothers were his closest successors:
Brother 1 - Don Baltasar Carlos de Habsburgo y Borbón - assassinated 1646,
no issue
Brother 2 - Don Felipe Prospero de Habsburgo y Habsburgo - died as child 1661,
no issue
Brother 3 - Don Fernando Tomás Carlos de Habsburgo y Habsburgo - died as child 1659,
no issue
By lack of brothers and their offspring, then
his sisters were his closest successors:
Sister 1 - Doña María Margarita de Habsburgo y Borbón - stillborn 1621,
no issue
Sister 2 - Doña Margarita María Catalina de Habsburgo y Borbón - died as child 1623,
no issue
Sister 3 - Doña María Eugenia de Habsburgo y Borbón - died as child 1627,
no issue
Sister 4 - Doña Isabel María Teresia de Habsburgo y Borbón - stillborn 1627,
no issue
Sister 5 - Doña María Ana Antonia de Habsburgo y Borbón - died as child 1636,
no issue
Sister 6 - Doña María Teresia de Habsburgo y Borbón (1638-1683) x Louis XIV de Bourbon, King of France
-----------------> Louis de Bourbon, "le Grand Dauphin" x Maria Anna Christina von Bayern
---------------------------> son 1 - Louis de Bourbon, "le Petit Dauphin "----> the French Bourbons
---------------------------> son 2 - Philippe de Bourbon, Duc d'Anjou ----> the Spanish Bourbons
Sister 7 - Doña Margarita de Habsburgo y Habsburgo x Leopold I von Habsburg, Emperor of Austria
------------------> Issue (the House of Habsburg in Austria)
Sister 8 - Doña María Ambrosia de la Concepción de Habsburgo y Habsburgo - died as child 1665,
no issue
Had all these brothers and sisters no issue at all, then we needed to look to the
paternal uncles of Don Carlos II
Uncle 1 - Don Carlos de Habsburgo y Habsburgo-Este - died in 1632,
no issue
Uncle 2 - Don Fernando de Habsburgo y Habsburgo-Este, "
El Cardenal-Infante" - died in 1641,
no issue
Uncle 3 - Don Alfonso de Habsburgo y Habsburgo-Este - stillborn 1611,
no issue
Now the paternal uncles of Don Carlos II had no issue, we need to look at his
paternal aunts:
Aunt 1 - Doña Ana María de Habsburgo y Habsburgo-Este x Louis XIII de Bourbon, King of France
-----------------> Louis XIV de Bourbon, King of France (making the Bourbon-claim even stronger)
Aunt 2 - Doña María de Habsburgo y Habsburgo-Este - stillborn 1603,
no issue
Aunt 3 - Doña María Ana de Habsburgo y Habsburgo-Este x Ferdinand III von Habsburg, Emperor of Austria
-----------------> Issue (the House of Habsburg in Austria)
Aunt 4 - Doña Margarita de Habsburgo y Habsburgo-Este - stillborn 1611,
no issue