European young men enlisted in the army because it was one way out of poverty. Catholic priests instructed the soldiers in mathematics, writing, theology, Latin, Greek, and history, and wrote letters and official documents for them. King's army officers taught military arts. An uneducated young recruit could become a military leader, elected by their fellow professional soldiers, perhaps based on merit. Others were born into hidalgo families, and as such they were members of the Spanish nobility with some studies but without economic resources. Even some rich nobility families' members became soldiers or missionaries, but mostly not the firstborn heirs.