Severe divine punishment does not fall upon a nation for ordinary mistakes. It is the result of a deep, ongoing denial of God's involvement in the world. When a society completely abandons its faith, God's response strikes at the very foundation of human existence, removing the basic necessities of life until survival itself is threatened.
The primary approach among commentators is that this level of betrayal is no common sin, but rather a fundamental treason. It represents a complete denial of God and His power, much like the people of Sodom and Gomorrah, who lived as though there were no ultimate justice or judge [רד״ק, מצודת דוד, ביאור שטיינזלץ]. Alternatively, this deep betrayal points to a pattern of repeated offenses. It is a rebellion that occurs over and over again until the moral decay is beyond repair [מלבי״ם].
In response to this profound rebellion, God strikes the land directly. This blow often comes through devastating natural disasters, such as blight, mildew, or severe droughts [רד״ק]. As a result, the society's food supply is entirely destroyed. Bread is metaphorically seen as a walking stick or staff because it supports and sustains the human heart. When God breaks this support, He is completely dismantling the land's sources of nourishment and stability [רש״י, מצודת ציון, ביאור שטיינזלץ].
The method by which this support is broken is through a devastating famine, ultimately leading to mass death [מצודת דוד]. Famine is regarded as the most severe of all divine punishments, representing the absolute peak of human suffering [מלבי״ם]. Furthermore, the devastation does not stop with humanity; it expands to wipe out the animal kingdom as well. The destruction of livestock and wildlife is not a punishment directed at the animals themselves. Instead, it serves to deepen the tragedy, intensifying the pain and the severity of the punishment for the people [רד״ק].