Final answer:
The Trojan prince who violated xenia in Sparta was Paris, who seduced and took Helen to Troy, leading to the Trojan War. This caused a major political shift, contributing to the decline of Sparta, which had to adapt from a militaristic society to a naval and diplomatic power.
Step-by-step explanation:
The Trojan prince who violated the concept of xenia in Sparta was Paris. Xenia is the ancient Greek concept of hospitality, especially as shown to those who are far from home. Paris abused the hospitality extended to him by King Menelaus of Sparta when he seduced Menelaus's wife, Helen, and took her back to Troy. This act of betrayal led to the Trojan War, a devastating conflict that resulted in the downfall of Troy.
The consequences of Paris's actions had a ripple effect. The war severely weakened both the victors and the defeated, changing the political landscape of the ancient world. It led to the eventual decline of Sparta, as it had to transform out of necessity from a land-based militaristic state, to a naval power engaging in diplomatic relations. The betrayal by the Trojan prince and his violation of xenia had far-reaching consequences that transcended the immediate story of the war itself.