Famines had occurred in Ukraine cyclically since the 17th century due to the challenges of non-collectivised management of agriculture, the appropriation of produce by land-lords etc. at approx. three to four year intervals. The 1931-1932 famine was the last famine in Ukrainian history.
Well, actually the 1946-47 famine was the last, and it was rather tame in comparison to previous famines. It can be mainly attributed to the devastation of WWII.
Produce shortages, compounded by weather effects, were further increased by deliberate sabotage on the part of kulaks who burnt crops and slaughtered livestock on a mass scale, in resistance to poorer peasants appropriating their land to form collective farms.
The entire concept is ridiculous. Many intentionalist narratives say that it was to stagnate peasant resistance to collectivisation, but it is obvious that a famine in any circumstance would do the exact opposite of this.
The entire concept arose from Ukrainian Nationalist propaganda and was perpetrated by mouthpieces of the Nazis, such as the Hearst press. Thomas Walker, the "eyewitness journalist" who wrote many pieces, had never visited Ukraine in the first place.
Changes in population growth statistics have been attributed by Conquest to be the result of a famine. However, it was not death rates that increased, but birth rates that decreased due to industrialisation and promotion of women in the workplace, free childcare, and contraception.
The 1931-1932 famine occurred in areas of Ukraine outside of the Soviet Ukrainian government, occurred in Poland, Belarus, the rest of the Soviet Union, and many areas of Central Asia as well. This was primarily due to weather conditions.