On Dec. 26, 1941, just 19 days after Pearl Harbor, Winston Churchill addressed Congress and famously raised the following question about the enemy, "What kind of people do they think we are?"

The more important question now is "Who do we think we are?"

Finding the answer requires a courageous honesty that goes to the core of what makes us who we are. It also provides a roadmap for how we address a variety of challenges that lie ahead.

Immigration is one such challenge. The issue goes to the heart of American identity and unity. People from around the world want to come here to escape poverty, oppression or other social ills. They come in huge numbers, and there is no sign immigration to the United States is slowing down.

Some 5.6 million people became U.S. citizens from 1991 to 2000. But in just the three full years since Sept. 11, 2001, we've naturalized more than 1.5 million people and made 3 million more lawful permanent residents nationwide. More than 10 million undocumented immigrants already are here, and about 1 million more arrive every year. California leads the world in immigration with legal and illegal immigrants alike.

How can people from different nations, who speak different languages, worship differently and practice different social customs settle in the same place without turbulence and strife? Our answer, historically, is to Americanize them - to integrate them by respecting some differences but melting most others so as to transform many people into one nation of Americans.

These challenges of immigration and assimilation are not new to us as Americans. We always have been more diverse - racially, ethnically and religiously - than most countries. We've always lived with deep differences. E Pluribus Unum (Out of many, one) is not just our national motto; it is our supreme American achievement. That said, we cannot take in the entire world, and it is essential that those who do come here must become American.

But, over the last 30 years, we've seen disturbing signs that, here in America, difference and separateness are becoming more pronounced than unity and harmony. Which is why I submit that immigrants must be "Americanized." They must be integrated into our society. We will respect some differences, but we will melt most of them into our culture, transforming them and us into something different and better.

Some question if this is still possible or even desirable. In the last generation, a growing chorus has come to decry the earlier transforming process. They have less confidence than ever that there remains any such thing as Americanism. Instead, they dwell on groups that supposedly have been locked out or left behind by the American Dream, and they stress our differences over what brings us together.

In fact, Americanization is crucial for American nationhood. It's how we survived the earlier waves of immigration - and went on to become a stronger nation with the help of those immigrants.

New arrivals saw themselves more as individuals rather than as members of a group. They saw themselves as looking forward to a new life rather than looking backward and clinging to old ways. They saw becoming an American as a matter of heart and mind rather than race and ancestry. And they saw themselves as part of something transformative rather than preservative.

So what do we do? We can't just throw open the borders in the name of diversity, as our liberal friends would have it. To do so would balkanize the nation, leave us divided and weak and enable multicultural dogma to triumph over American identity and purpose.

But neither can we shut down the borders in the name of security and efficiency, as many of our conservative friends would prefer. Relying strictly on law enforcement may seem like sound public policy, but it ignores the genius of what makes us Americans - and, in the end, it won't work.

What we can do is establish a path to citizenship that is clear, open and rewarding.

We should establish a system whereby people who want to live here legally leave, then apply to return. We cannot reward lawlessness, and we must reward those who play by the rules. We should forge agreements with key nations to facilitate the return of their citizens and reward those that develop programs and policies that reduce the unlawful population in the United States.

We should engage nongovernmental organizations to establish humanitarian support programs to help undocumented workers return to their home countries. And we should establish a system whereby undocumented workers who have no criminal record and voluntarily leave the country after registering with authorities can apply for legal entry without prejudice.

And finally, we should establish a citizenship education program that helps them think of themselves as Americans.

The challenges of character forming, culture blending and nation building are greater than ever, but we can meet them. And we must. At stake are the guardianship of freedom and the continuation of our uniquely American legacy.

Simon is co-chairman of William E. Simon and Sons L.L.C. This article is based on a lecture he delivered at The Heritage Foundation (heritage.org).