Only when faced with a profound and present threat do people leave all they know and sacrifice all they own, splitting up their families in hopes of finding safe haven. Only in desperation will we entrust our life savings to dubious traffickers and pile onto an overloaded boat or the back of a covered truck with neither a clear destination nor a sure refuge.

The refugee crisis now infiltrating Europe is of mammoth proportions and will not let up anytime soon. The only choice is to carefully screen and welcome as many as possible, but that is only the beginning. New immigrants will need shelter, education and health care. Most important, they will need an opportunity for a better life. To deliver, it will take open hearts and minds, tremendous resources, great resolve and time. If done well, the respectful assimilation of newcomers will make Europe stronger and healthier than ever before. The alternative is unspeakable.

Angela Merkel, Germany’s chancellor, has invoked the principle of “willkommenskultur,” the European version of aloha. Refugees must be welcomed because it is morally right and the only compassionate course of action. We must act in the same manner we would hope to be treated were the tables turned. New immigrants are also sorely needed and have as much to offer their new hosts as they might wish to receive. Why? Like most of Europe, Germany has a fertility rate of 1.6 — far below the 2.1 needed to maintain a stable population. In fact, most affluent nations are facing a graying society and are hard-pressed to keep up with entitlements for health care and retirement income. The ability to maintain their social contracts and preserve productivity depends entirely upon new, young and capable workers to fill jobs at every level.

Some years ago I attended a briefing at the U.S. Embassy in South Korea to discuss lessons of the reunification of East and West Germany after the fall of the Berlin Wall. The process of integrating people with different social biases, varying degrees of education and unique perspectives on government must be decisive but gradual. Parity cannot be offered immediately. Comprehensive inclusion might take a generation. Successful integration is achieved neither by futile efforts at achieving homogeneous assimilation nor by xenophobic segregation, which only ensures health and wealth disparities. Immigrants must be motivated to join the ranks of responsible, loyal citizens as they build their new lives and learn to trust that ethnic and religious diversity will be expressly accommodated.

It will not be possible to take in all of the huddled masses yearning to breathe free, and intentions will not be uniform.  The Islamic State and other organizations will attempt to embed terror cells into the mass migration toward Europe. Enemy combatants will need to be rooted out. There will be many disappointments along the way, but care must be taken to avoid a two-tier segregated society, which would only lead to the dangerous predicament depicted by “Les Miserables.”

Despite its challenges, in particular averting a “grexit,” or Greek exit, of late, Europe already has come far, first in unifying Germany and then in creating a monetary union while gradually expanding the number of member nations. The EU has enabled the free flow of labor, which means that today Europeans from diverse nations are readily crossing borders, effecting a free flow of labor in their pursuit of liberty.

The U.S. is still seeking its own durable strategy to manage economic migrants from Latin America. The Western Hemisphere also must find a way to establish a fair pathway to citizenship and invest in education that includes teaching them English to prepare our immigrants to proudly join the workforce. In fact, without the current Hispanic population in the U.S., the fertility rate would be 1.8 and, like Germany, too low to maintain a steady population. With the benefit of Hispanic immigrants, the U.S. will continue to grow at a healthy rate, enough to support the needs of an aging population for the long run.

The current crescendo in human migration to Europe from the Middle East and Africa ultimately could exceed that at the end of World War II. It is a high-stakes challenge to the founding principles and institutions of modern liberal society. The world order depends on our collective ability to rise to the occasion. In the meantime the principles of democracy, the promise of liberty and the spiritual practice of compassion will be put to the test.

Ira Zunin, M.D., M.P.H., M.B.A., is medical director of Manakai o Malama Integrated Healthcare Group and Rehabilitation Center and CEO of Global Advisory Services Inc. Submit your questions to info@manakaiomalama.com.