THIMPHU, Bhutan—This secluded Buddhist kingdom uses a unique barometer to measure economic progress. And the message of the 2015 Gross National Happiness Index is a troubling one: Money isn’t buying enough contentment.

Tucked high in the Himalayas between India and China, Bhutan was poor and largely closed to foreigners when its fourth king declared, in the 1970s, that “gross national happiness” was more important than gross domestic product, or GDP.

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