In Nishmas said on Shabbos and Yom Tov mornings we say, “you redeemed us from Egypt and delivered us from the house of bondage; you fed us in famine” (all describing times of trouble) “and sustained us in plenty” (not normally thought of as a time of trouble), “you delivered us from the sword saved us from the plague and spared us from serious and lasting illness” (more trouble).
What is “and sustained us in plenty” doing there?
In times of plenty, there is a risk of losing sight of Hashem and abandoning Judaism. Sustaining us in plenty, means that even when things were good, and the Jewish people were not being forced into otherness by the evils around them, Hashem kept them together and faithful.
"Times of plenty" can be referring to the wealth of the nation that the Jews are living in, and not the wealth of the Jews themselves. Sometimes in history, the host nation would tax the Jews out of all that they owned, making the Jewish people poor. Despite the wealth around them, the Jewish people felt that they were mainly getting their sustenance from Hashem.
There are other ways of reading this as well.
(Answering my own question). I just now found in the Siach Yitzchok (in the Siddur Ishei Yisroel) that the passage beginning with "bero'ov zantonu" reckons out in order the miracles that occurred for those who left Egypt.
Until the 15th of Iyyar they suffered increasing hunger (bero'ov) but they were fed (zantonu) from the matzo they took out with them. Then HaShem provided the "mon" (ovasovo kilkaltonu - sustained us in plenty) because the mon was blessed in their stomachs satisfying them.
He delivered us from the sword (of Amolek) and saved us from the plague (Bamidbor 17 (13)).
He spared us from serious and lasting illness. This, he says, is deliverance from snakes and scorpions.
So my question was wrong. The unifying principle in these items is the miracles that occurred for those who left Egypt.
