The answer is: Ammon

Jeremiah 49:1 - In this verse, the Prophet Jeremiah declares God’s judgment on Ammon, which had its territory to the east of Gad. This highlights the shifting alliances and enmities in ancient Israel. Interestingly, Gad's warrior heritage is explored in Numbers 32:1-5, showcasing their role in defending Israel while often facing hostile neighbours like Ammon.

When we delve into the fate of the tribes of Israel, it's fascinating to see how the dynamics of geography and ancient alliances shaped their stories. In the case of Gad, the mention of the Ammonites by Jeremiah brings to the forefront an age-old rival distinct from many others encountered by Israel. Gad, known for its fierce warriors, was situated at a pivotal location stretching along the Jordan River, confronting the expansive territories of powerful neighbors.

The Ammonites, descendants of Lot's youngest daughter, had their own rich history, often clashing with Israel. In addition to the prophetic words of Jeremiah, we could think back to other moments involving these peoples. For instance, the Book of Judges recounts conflicts with the Ammonites led by Jephthah, further highlighting the volatile relationship they had with Israelite tribes.

Trivia tidbit: The name 'Gad' means ‘good fortune’ but is also associated with war, as indicated by the tribe's characteristics noted in the blessings of Jacob and later in Moses’ blessings. Perhaps it’s everything but coincidental that while some myths and fortunes hook to brave warriors, the lineage of conflict seemed to cast a long and tumultuous shadow over this land.

So, while Rocha by the powerful Jordan River offered both prosperity and challenge, events foretold in the prophetic scrolls maintain an enduring relevance, reminding us that ancient treasures hold stories of constant struggle and resilience, vividly echoing through today.