India, May 6 -- The postcards are still hanging in the windows of travel agencies from Berlin to Barcelona: blue Mediterranean coves, Greek ferries at sunset, crowded piazzas in Rome, island flights skimming over turquoise seas. But behind Europe's glossy summer tourism campaign, a different image has begun to take hold - airport departure boards blinking red with cancellations, fuel traders watching tanker routes hour by hour, and small family-owned hotels wondering whether another geopolitical shock could undo a season they spent all winter preparing for.

Across Europe and much of the world, the expanding crisis tied to Iran, aviation disruptions and instability around the Strait of Hormuz is increasingly being viewed not merely as a r...