Not true. First of all, I doubt you have an army, Second all modern monarchies had some sort of legal claim. Sure, the winner wasn't always the one with the stronger claim, but just because a good lawyer can win an unjust lawsuit, his client needs some argument. War was and is a way to settle a dispute.
Henry Tudor was declared King by right of conquest, but he still was related to the Plantagenets and more importantly all the Plantagenets were dead. There was no way to decide between the remaining relatives, because the rules of inheritance weren't settled.
In the case of the Spanish War of Succession, the rightful heir was blocked by war, which was almost pure realism (Austria claimed the Spanish throne with an argument that I found weak, but was still an argument.) However, the result was a family member of the heir was chosen.
Napoleon Bonaparte introduced the idea of a plebiscite to establish legitimatize his power grab. Other new monarchs have received their thrones from a legislature, the nobility, or as the result of international law. They are either members of a royal house, or leaders of the war of independence.
