There are certainly noticeable differences between people from different parts of the world. These differences are the result of adaptations to the local environments. Humans evolved in Africa 200,000 years ago. Many Africans from different regions are quite different from each other. Some, like the African pygmies, are quite short in stature. The East Africans in contrast are quite tall and lean. The West Africans tend to be more muscular. Non-Africans tend to overlook these differences but they are adaptations to a local environment. Being short for example minimizes surface area and being tall maximizes it. People who live in forested regions tend to be shorter because those environments are cooler and the reduction in surface area can help them conserve heat, while tall and lean people with long arms and legs can avoid heat stroke more easily by losing excess body heat more quickly.
About 60,000-70,000 years ago, Africa suffered a severe drought, and a small group of Africans migrated out of Africa and populated the rest of the world. All non-Africans evolved from this group of migrants. The first places these migrants went to was SE Asia. There they largely remained unchanged. The descendants of these first migrants are still very similar to Africans in having dark skin, curly hair and no body hair, except under the armpits and in the pelvic region.
Other people however have changed. These people are descendants of the early migrants that settled in Central Asia (near Kazakhstan) instead of going all the way east to SE Asia. After 20,000 years in Central Asia, some of them migrated to Europe and adapted to ice age conditions by becoming more hairy, shorter, with shorter arms and legs, thinner lips, taller and narrower nose bridges, straight hair, a rounded torso, and more fat under the skin. These are adaptations to cold climates. They reduce body surface and also reduces air flow in and out of the lungs to prevent frost bite of lung tissues.
Some Central Asians migrated to northern Asia, where they also evolved many of the same adaptations to cold climates seen in Europeans. Therefore it is sometimes difficult to distinguish a cold adapted Asian from a European. Both groups evolved light skin tones because their cold environments force them to wear clothes, which block out the sun and reduces vitamin D production. Vitamin D shortage can result in rickets, with broken or deformed bones and even death as consequences. Light skin helps them absorb enough sunlight to avoid rickets.
If people were to stop migrating after they settled in Europe and Asia, then it would be relatively easy to define races, which are differences within a species that is based on geography. To this day, it is still relatively uncontroversial to recognize 3 different races, known as Caucasoid, Africanoid and Mongoloid. However, people have not stopped migrating, not by a long shot. Some Europeans for example migrated back to the Middle East and some went as far west as the Indian subcontinent. The Chinese also migrated south to SE Asia. Everywhere people went, they intermixed with each other. This admixing is strong evidence that we are all the same species. SE Asians are a mix of the dark skinned early migrants and the cold adapted Chinese from north of the Yangtze River. Indians and Middle East people are a mix of dark skinned natives from Africa and light skinned Europeans. Such admixture makes it nearly impossible to classify some groups of humans from some regions as a particular race.
In any case, since the different traits we see in different people are simply the result of adaptations to different local environments, it really does not matter much where people or their ancestors came from. We are all human. We recognize each other as the same species. Therefore it really makes no difference whether we can divide the human species in to different races or not.