Final answer:
Americans feared Germany's exclusive rights in Kiao-chao could threaten U.S. interests and stability in Asia, impacting America's Open Door Policy in China.
Step-by-step explanation:
The Americans feared that Germany's exclusive rights in Kiao-chao (Kiaochow) might result in the expansion of German power in Asia, potentially threatening American interests and contributing to instability in the region. Such rights, akin to a sphere of influence, granted Germany significant control over the area, which could be used to disrupt the balance of power, impede American commercial interests, including the principles of the 'Open Door Policy' in China, and lead to further aggression that could draw other nations, including the United States, into a broader conflict.