Yaakov Avinu's vow to give a tenth of his wealth to Hashem (28:20-22) is a model for all of us in times of crisis (Medrash Rabbah 70:1). The Rambam (Taaniyos 1:1) records a Torah commandment to pray and sound trumpets when the community faces a crisis. If the community recognizes that the difficult situation results from their misdeeds and do teshuvah, the crisis will be lifted. But, if they do not pray, and attribute their plight to chance, their troubles will increase.
The mitzvah of sounding trumpets applies in times of crisis, as well as in days of joy and festivals when offerings are brought (Bamidbar 10:9-10). The Magid Mishnah asks why the Rambam did not count the two seemingly unrelated instances when we are obligated to blow trumpets as two separate mitzvos.
Perhaps Rambam's reason for the mitzva provides the answer. The purpose of sounding the trumpets is to proclaim our belief in Hashem's providence. Just as we declare that crisis is not a chance event, but something decreed by Hashem, so too must we demonstrate our recognition that joy and festivals are blessings bestowed by Hashem. It is this common theme which is the essence of the single mitzva of the trumpets.
A similar idea can explain the view of the Rambam concerning prayer. In the Sefer Hamitzvos (Aseh 5) he states that the Torah commands us to pray in a time of crisis. The Rambam interprets "mikra kodesh" (Vayikra 23:2) as a communal mitzva to pray on holidays with joy and hallel. Prayer, like trumpets, in situations of extreme crisis and celebration reflects the realization that both are decreed by Hashem.
In America, Am Yisroel has been blessed with security and great prosperity. As the nation expresses thanksgiving, we certainly must thank Hashem for protecting and blessing us. Yet, America faces an unprecedented crisis of terrorism which threatens both our security and prosperity. For us, the terrorism in Eretz Yisroel is a source of perennial concern.
In times of crisis we should give tzedakah, as Yaakov Avinu did, do teshuvah as the Rambam rules, and daven with greater intensity, as the Rambam states. Uteshuvah, utefilla, utzedaka maavirin es roah hagezeira."