A soldier with Ukraine’s 77th Brigade looks at a piece of sighting equipment on April 21 on the outskirts of Chasiv Yar in Donetsk Oblast, Ukraine. (Ed Ram for The Washington Post)

Regarding Mark Hertling’s May 17 op-ed, “Why Ukraine hasn’t counterattacked just yet”:

The war between Russia and Ukraine is the ongoing, life-or-death case study of a live, as-it-happens, conventional (nonnuclear, so far) war between two nations with crucial worldwide implications and heavy, if indirect, U.S. participation. This is an extremely rare, almost World War I-style military battle that war colleges must be studying minute by minute around the clock and will continue to study for many years to come.

The motivational and other psychological factors involved in this war are as important as the physical tactics and weaponry involved.

Ben Lacy, Washington

The excellent May 18 editorial “How to protect Ukraine — after the war” fell short in one respect.

I strongly believe that the United States should enter into a security treaty with Ukraine to deter another Russian invasion. We did so with the Republic of Korea when United Nations forces negotiated a cease-fire on the Korean Peninsula in July 1953.

That cease-fire has held for 70 years, and the treaty has deterred attacks by China and its North Korean ally.

Richard W. Murphy, Bethesda