The time predating the first elected king was characterized by unrest and injustice - brute force ruled.
To restore law and order the German princes decided to institute a freely elected king from among a specific group of Electors. Three ecclesiastical and four lay princes would elect the first German king.
They preferred a candidate from one of the weaker houses as that would enable them to negociate privileges and political influence. For these reasons they also wanted to intermix the crown dynasties.
The elected prince had therefore an interest in making the most of his period of office and expanding his own power.
The House of Habsburg proved to be particularly skillful during these hard times. Rudolf I von Habsburg was elected King in 1273 - as a congenial but not particularly affluent noble.
With skillful matrimonial politics, intrigues, alliances and at least partly, annexation of conquered territories, the Habsburgs became more and more powerful through the centuries, and despite this still managed to present royal candidates who were too good to dismiss.
A coronation in March 1452 by Pope Nicholas V finally crowned Friedrich III von Habsburg Emperor of the Holy Roman Empire.