This is an intriguing question. The first twenty lines of Robert Frost’s poem “Birches” might – just might – conceivably be related to World War I in a number of ways. Since the poem, thematically, deals with the issue of lost youth, it is at least possible that the work may have some relevance the one of the most destructive, tragic wars in human history – a war in which countless young people died for little reason. If the birches are seen as young people who become bent (both physically and mentally) and crippled (both physically and mentally) by their war-time experiences, then the poem may indeed be relevant to the lingering effects of World War I on the many young people who had to take part in that conflict.
The poem’s first two lines imagine birches bent down, temporarily, by childhood play – by boys swinging in the birches so that for a time the trees lose their straightness. Yet the speaker then proclaims that
. . . swinging doesn’t bend them down to stay
As ice-storms do. (3-4)
If the ice-storms are associated with the effects of war, which alter the young forever, then perhaps the poem can be read as some kind of allegory about the effects of war. Especially intriguing, in light of this possible interpretation, is the statement that
. . . once they are bowed
So low for long, they never right themselves . . . (15-16)
Such phrasing might conceivably be related to the long-term effects of war. One might even read line 9, with its reference to cracking, as a reference to the destructive effects of war. Line 12, with its reference to shattered glass, can be read in much the same way. Likewise, line 14, with its reference to branches being dragged away by the load, might also be interpreted in this fashion, especially considering the horrific numbers of young people who were slaughtered in World War I.
On the other hand, some of the phrasing in the first twenty lines (as well as later) suggests that the speaker finds the bent birches (even the ones that are permanently bent) beautiful in various ways. Moreover, in the rest of the poem, he deals primarily with the birches that are not permanently bent. Also, the poem seems to have been written in 1913-14. World War I did not begin until August of the latter year, and the truly destructive nature of the war did become apparent until later. The poem was first published in August of 1915, and so it is possible that some of its first readers saw some connection between the poem and World War I. The poem can be more plausibly interpreted, however, in other ways. If Frost had wanted to make some connection to World War I, surely he could have offered more obvious hints. Any attempt to interpret the poem in the way you’ve suggested would need to be very carefully made. Still, you have given me something to think about, for which I thank you!