When the terror attacks unfolded this weekend in Israel, the first instinct of many Jewish Americans was to reach out to family and friends. Israel is a small country — you can drive from the top to the bottom in under six hours — but it is home to one of the world’s largest communities of Jews, who make up just 0.2 percent of the global population. The other largest Jewish population lives in the United States, and connections between the two groups run deep. Many Jewish Americans have relatives and loved ones who live in Israel, where, due to...