That's because the two countries have been really close and claiming that there's no "actual" difference between the two countries, and since Russia was in charge of Ukraine's territory,multiple times through history and is smaller, people called it Little Russia. hope it helps.
DescriptionInternational trade is the exchange of capital, goods, and services across international borders or territories because there is a need or want of goods or services. In most countries, such trade represents a significant share of gross domestic product. Wikipedia
Most of those major cities are located near Petroleum Fields and Coal Mines.
