Yet perhaps just as crucially, a major Russian incursion would also affect the flow of goods from Ukraine, the world’s fourth-largest supplier of wheat and corn. A major disruption of Ukrainian exports — especially in conjunction with any interruption in even larger Russian grain exports — could pile onto a global inflationary cycle that in many countries is already the worst in decades.

Concern is especially focused on fuel and food. Last year, global food prices surged 28.1 percent to their highest level in a decade, according to the United Nation’s food agency. Worries of war have already driven U.S. corn futures to their highest levels since June and sent wheat futures to two-month highs before a recent easing.

Over the past 20 years, bountiful Ukrainian harvests boosted the country’s role as a global breadbasket. Some of its biggest clients are economically battered, war-torn or otherwise fragile states in the Middle East and Africa, including Yemen, Lebanon and Libya, where grain shortages or cost surges could not only deepen misery but churn up unpredictable social consequences.