Final answer:
Poverty is a major factor influencing the development of chronic illnesses due to its associated lack of access to health care and other resources, poor nutrition, and increased stress.
Step-by-step explanation:
The major factor that has a major impact on the development of chronic illness is poverty. Poverty can lead to a variety of detrimental health outcomes due to factors like lack of access to health care, inadequate nutrition, and increased stress levels. These elements can contribute to the higher prevalence of diseases and health conditions among those who are impoverished. In contrast, factors like social stability, urban dwelling, and possessing a high school diploma do not have as direct or significant an impact on chronic disease development as poverty does.