Bella gerant alii, tu felix Austria nube - 'Let others wage war: thou, happy Austria, marry'.
Wikipedia doesn't say too much on the topic; but it's a frequently repeated historical anecdotal phrase.
What exactly was the origin of this foreign policy in Austria; and why was Austria special among other European powers (including other Hapsburgs) that they both tried and succeeded in it?
MOST countries' kings practiced "Diplomacy by marriage." Austria stood out by making it work. That's because her kings' marriages seemed to be highly topical, rather than random.
For instance, there didn't seem to be much of a point for Maximilian of Austria to marry Marie of Burgundy. Until you realize that Austria is on the southeast edge, and Burgundy/Netherlands was on the northwest edge of the Holy Roman Empire, and Maximilian was likely to (and became) Holy Roman Emperor.
The marriage of Maximilian and Marie's son Philip to Ferdinand and Isabella's daughter Juana didn't seem to make much sense either, until you realize that Spain and the Netherlands were on the south and north of their common enemy, a newly united France.
A couple generations later, the marriage of Austria's Prince Ferdinand to the heiress of Bohemia didn't seem to have to particular meaning, until one realizes that it enabled Austria, Bohemia, and the Holy Roman Empire to split off from Spain and the Netherlands (the latter two under Philip II).
On the other hand, the marriage of Philip II of Spain to England's Queen Mary didn't do much for either, except to arouse antagonisms on both sides. And the marriages of various French kings to Polish princesses didn't do much for France, because Poland was a liability, rather than an asset to France, given all her enemies. The marriages of French Louis (XIII and XIV) to Spanish princesses didn't reconcile these natural enemies.
Adam Smith in An inquiry into the Nature and Causes of the Wealth of Nations noted:
[W]hen land was considered as the means, not of subsistence merely, but of power and protection, it was thought better that it should descend undivided to one. In those disorderly times, every great landlord was a sort of petty prince. His tenants were his subjects. He was their judge, and in some respects their legislator in peace and their leader in war. He made war according to his own discretion, frequently against his neighbours, and sometimes against his sovereign. The security of a landed estate, therefore, the protection which its owner could afford to those who dwelt on it, depended upon its greatness. To divide it was to ruin it, and to expose every part of it to be oppressed and swallowed up by the incursions of its neighbours. The law of primogeniture, therefore, came to take place, not immediately indeed, but in process of time, in the succession of landed estates, for the same reason that it has generally taken place in that of monarchies, though not always at their first institution.
On what basis d you believe that the Austrians practiced diplomacy through marriage any better, or more or less frequently, than any other male-preference primogeniture nation? For a simple start, consider the many European Wars sub-titled of Succession, such as:
War of Austrian Succession
- War of Spanish succession
- War of Bavarian Succession
- War of Polish Succession
- War of Breton Succession
All of the above had a Hapsburg (or in the case of Castile a pre-Hapsburg) belligerent.