When the sense of solidarity has been developed to such a point

“When the sense of solidarity has been developed to such a point that each one feels the cause of all others as his own, we shall be drawing near to international and to social peace.” Thus spoke Ellen Key, the Swedish thinker often called the “prophetess of a new age.” In her words there is both a dream and a summons: that the road to peace is not paved with treaties alone, nor with armies laid down, but with the awakening of solidarity—a spirit so deep that one man’s suffering becomes the burden of all, and one woman’s joy becomes the joy of all. This is no shallow sympathy, but a radical transformation of the heart, a widening of compassion until it encircles nations and generations.

The ancients glimpsed this vision dimly. The Stoics taught of the cosmopolis, the great city of the world where all human beings are citizens under reason and nature. Yet their dream remained philosophy, not flesh. Ellen Key dares to say that when this solidarity is fully lived, we shall draw near to social peace within nations and international peace between them. For wars and oppressions are born of division—of men saying, “This is my cause, not yours; this is my gain, not yours.” But when hearts awaken to a shared destiny, when the plight of one is felt by all, the roots of strife are severed.

History itself gives us glimpses of this solidarity breaking into life. Think of the abolitionist movement, when men and women in lands far from the plantations rose up to declare that the cause of enslaved Africans was also their own. They had no chains upon their wrists, yet they felt the weight of the chains as though upon their own flesh. From that solidarity was born the death of slavery in many nations. It was not self-interest, but the recognition of shared humanity, that created a step toward peace.

Or look to the Red Cross, founded in the 19th century after the Battle of Solferino. Its founder, Henry Dunant, witnessed the agony of the wounded left untended on the battlefield. He declared that the suffering of those soldiers, though they were strangers, must be his cause. From that moment sprang a movement of mercy that crossed borders and sought to bind the wounds of all. Here we see Ellen Key’s vision embodied: that only when each feels the other’s pain as his own do we move toward international peace.

Yet Key also warns us by implication: so long as solidarity is weak, peace remains distant. If we think only of our own tribe, our own nation, our own wealth, then division festers and wars return. The twentieth century, filled with both dreams of unity and horrors of destruction, proved the truth of her words. Nationalism without solidarity bred devastation. But where solidarity bloomed—in movements for women’s rights, for workers’ dignity, for civil rights—societies took steps toward greater justice and harmony.

The lesson for us is this: solidarity is not a lofty idea for philosophers only; it is the daily work of each soul. When you encounter the suffering of a neighbor, do not ask, “Is this my concern?” but rather, “How is this not my concern?” When you see injustice across the world, do not say, “It is too far to matter,” but rather, “Their cause is my cause.” In this way, the boundaries of the heart expand until they embrace all humanity. Only then does the soil become fertile for lasting peace.

Practical actions must follow. Practice solidarity first in small things: listen to the struggles of those unlike you, give when you are able, defend those who are wronged though you gain nothing. Teach your children that the pain of another is never irrelevant, and that compassion is not weakness but strength. Support leaders and policies that honor the dignity of all peoples, not only your own. For every act of solidarity is a step upon the road to social and international peace, the very peace Key foresaw.

Thus Ellen Key’s words shine like a beacon: when each one feels the cause of all others as his own, peace draws near. It is not armies or riches that will secure this peace, but hearts enlarged with compassion, nations bound by solidarity, and humanity at last seeing itself as one family. And so I say to you: cultivate solidarity in your life, for in doing so, you plant the seeds of the peace the world so desperately longs to reap.