The period of history from the 5th to the 15th century was known as the Middle Ages. During this time, the law of the land in Europe was known as the "feudal system". This was the manner in which the upper 5% (the nobility) controlled the lower 95% (the serfs or peasants). Other crucial contributors to this structure were the leaders of the church.
There were a few kings who were very wealthy and powerful, who owned all of the land. To maintain control of this land, it was broken into fiefdoms and pieces were given to friends of the kings (barons). The barons then allotted land to their friends and allies in order to govern efficiently. It was in this manner that the "nobility" was created, and the land passed down through these select few families by manner of inheritances. The reward of being delegated this control came at a price. To maintain the control of the fiefdoms, manors and estates, the nobility had to pledge fealty to the kings and pay them taxes and homage.
Most peasants were provided with a small shelter on a small piece of land and the "protection" of the noble in charge of that area. In return, they worked for the estate, farming the land, paying taxes and having little control over their own lives. Some peasants were "free" and had their own small businesses: blacksmiths, carpenters, bakers, etc. They paid for the protection of the lord with money, goods and services and were obligated to use (and pay for) services of the manor like mills or large ovens.
The decline of feudalism made the nobility less important. This was partly because of the rise of the middle class, which included commoners who were as wealthy as many members of the nobility. And it was partly because they had lost their military importance as knights became vulnerable and standing armies reduced their value as a first response. Ultimately, this made life a bit easier for the nobility, as they did not have quite as much responsibility, but were able to buy luxuries supplied by the middle class merchants.
Most nobles' wealth derived from one or more estates, large or small, that might include fields, pasture, orchards, timberland, hunting grounds, streams, etc. It also included infrastructure such as castle, well and mill to which local peasants were allowed some access, although often at a price. Membership in the nobility was usually a prerequisite for holding offices of trust in the realm and for career promotion, especially in the military, at court and often the higher functions in the government and judiciary.
Almost all nobles were knights. Training began at age 7 as Pages. They would become Squires (Knapen) at age 15 and were then trained by other Knights. At age 25 they became "of age" (girls at age 20) and could become a knight after their father had passed away.
All marriages were arranged between nobles. Read here about marriage customs at that time.
The demise of Dutch nobility:
In the 15th century, as towns grew and new social structures and guilds emerged, the power of nobility and clergy diminished. Cities created their own autonomy and judicial privileges and appointed magistrates and important council positions, which the nobles had always kept for themselves. This was the beginning of the end of feudalism and the power of knights.
Already in 1481 (Guelders) nobles were not really recognized by the Burgundian rulers and their regular biannual meetings (Landdagen in Arnhem) were now forbidden. To protect themselves from the new influence of nobles from other regions (e.g. Cleves), the Guelders nobles decreed that one could only be written into the Guelders nobles charters if one was born there. After William of Cleves lost his power war against Charles V in 1543, the Guelders nobility was doomed. A new "Stadhouder" was now the ruler of the land and Dutch nobility virtually expired and what was left was abolished during Napoleon's occupation.
Some of the van Ossenbruchs in the county of Cleves and Gulik (not occupied by the Spanish) maintained their titles. For example; Johan (the son of Vincentius), Lord of Blitterswijck (20 km North of Venlo), was not only listed as one of the most important knights in Gulik in 1591, but was also registered in the Guelders' Overkwartier knighthood in 1592.
The van O-s, in de Achterhoek and Arnhem areas, do not seem to be registered, although Otto van Ossenbroek's son-in-law Cornelis van Sallandt, mayor of Arnhem, was written into the "Riddercedul" from 1575-1607. The other Van O-s probably went from "Gentry to Cavalry" (Ridders tot Ruiters) in one or two generations. Read more about that on the 1600-present tab --> Towns --> Arnhem page.
However, after Napoleon's defeat the new Netherlands got a new King in 1815: Willem I. He created most of the present Dutch nobility from old Dutch native regents- and patrician families.
In the newly drawn up list of nobles in Holland in 1814, there were not any O.'s (with any of the various spellings) listed.