I was wondering what the relationship between the two was. Philip was king of Spain but also held several titels in HRE (in the Netherlands). Maximilian was his uncle and the emperor of the HRE. I was wondering what their relationship was in the light of the reformation and eighty years war. Maximilian was emperor of both Catholics and Protestants after all. Filips was however a hardline Catholic and was essentially purging protestant dissidents.
/u/dinobilly
First of all, Maximilian II is a cousin of Philip II, not an uncle. (And not both, haha.)
By the time of Charles V's abdication, there was a major divergence in the strategic views of the Spanish Habsburgs and the Austrian Habsburgs. In 1548, advised by his advisor Granvelle, Charles had wanted for his son Philip to succeed him as HRE emperor as Philip had access to the vast wealth from the Americas. This was greatly opposed by Ferdinand his uncle, the brother of Charles V. Charles then proposed a back-and-forth shared emperorship between the two branches, which was also rejected. As soon as Charles abdicated, Philip repudiated all his claims to the Austrian side, setting a favorable relationship between the two sides.
The above set the tone of the rule of the junior line of Habsburgs in Austria, who was always in a position of relative weakness, especially financially. While Ferdinand had obtained kingship of Hungary, this required significant military and financial commitment to bolster defense against the Ottomans. This led to weakness relative to electors, of whom several were Protestant, thus forcing significant compromises. This is a big factor in what led to the Peace of Ausgburg. The secret Declaratio Ferdinandei was written specifically to accommodate Protestant imperial knights, even if we know later on that this peace was untenable in the long term.
In the early period of his rule, Philip was cultivating a northern orbit with England as part of the constellation. After all, he was married to Mary Tudor and was himself King of England. Both Mary and Philip were deeply faithful Catholics and wanted to reform the church in England and in the Low Countries, recognizing the degree of corruption and the spread of heresy. In the end, Mary's untimely death undid all the work in England, and forced Philip to be accommodating toward Elizabeth as he focused on the Low Countries. Unfortunately, his reforms of the church there led to enmity from corrupt church leaders and from nobility.
Taking the above into account, it is no wonder that the Austrian Habsburgs tended to avoid mingling into Philip's affairs in the Low Countries. Both Ferdinand and Maximilian II followed this line, never actively helping Philip's attempts to subjugate the Dutch revolt.