BARCELONA, Spain — On Sept. 11, 2012, Catalonia’s national day, about 1.5 million people marched through Barcelona carrying banners saying “Catalonia, Europe’s Next State.” The march was a peaceful expression of hope. On Wednesday, with the same purpose, hundreds of thousands of people will form a human chain across Catalonia.

The history of Catalonia goes back centuries, when Iberian tribes traded with Greeks and Carthaginians along the Mediterranean coast. An identifiable Catalan culture developed in the Middle Ages and has strengthened through time, despite the loss of the Catalan sovereignty at the end of the War of Spanish Succession in 1714, and the subsequent repeated suppression of our government, schools, language and values.

Catalonia fought hard to defend the Second Republic in the Spanish Civil War from 1936 to 1939. But democracy and autonomy were crushed and the Catalan language was made illegal as Spain endured 40 years of brutal dictatorship under Franco....