Steinbeck's view of humanity is that people are a product of their socio-economic system. His novel advocates for a world in which it is easier for people to be good because social and economic structures are in place that treat people humanely and provide for their basic needs. People have a basic worth in his eyes just because they are human.

In a dog-eat-dog capitalist system based on competition, people will engage with each other in a brutal fight for survival. If people are taught that other people are widgets to be used for their own gain, they will respond by doing that. Steinbeck critiques the heartlessness of a system that drives people like the Joads away from their homes during the Dustbowl and then exploits them mercilessly.

Steinbeck is exposing the cruelty of the capitalist world of the Great Depression in which people had no protections against exploitation, such as the minimum wage, which did not go into effect until 1938. He advocates for the kind of cooperative system the Joads encounter at one migrant labor camp, where people are encouraged to work together, and children are ostracized for overly competitive playground play. His ideal view of humanity is one of cooperation so that everyone can prosper.

The Grapes of Wrath has many different messages about humanity laced through it, so to argue that Steinbeck had any one view might be too limited. However, looking at some of the themes of the book gives us a good idea about his personal views.

The characters in the book struggle from beginning to end. The almost impossibly harsh challenges they face has been seen as Steinbeck's interpretation of the human condition. He also chose to show these characters helping one another in these times of need and...

that "all people essentially belong together and are a part of one another and of a greater whole that transcends momentary reality, is what removes The Grapes of Wrath from the genre of timely proletarian fiction and makes it an allegory for all people in all circumstances" (eNotes)

We can see that Steinbeck likely felt that humans cause each other unimaginable suffering and pain, but that humanity is also capable of great kindnesses and compassion toward one another. So, he presents two versions of humanity—the predator and the prey. However, that he focuses so strongly on the "prey," if you will, via the Joad family, shows us that he viewed humanity as strong, compassionate, resilient, and even generous.

In The Grapes of Wrath, what does John Steinbeck show about mankind's connection to others?

Steinbeck's overall message to humanity is about the ability to transform reality.  Steinbeck uses Tom Joad to show how someone who is self- exiled, seeking to not look after anything other than their own interests can rise to being a collective being and be an agent of change.  The loudest point that Steinbeck makes is that individuals do not have to be chained to their existence, modeling what it is.  They have the power and can make conscious choices on any level in order to transform their world into what it should be as opposed to what is might exist as.  In the time period of the Great Depression, this is a poignantly powerful message.  Tom Joad recognizes that he is a part of something larger than herself. Ma Joad recognizes that she is a part of something larger than herself.  Even Rose of Sharon with the last action of the novel finally acquiesces to the idea that she is part of something larger than herself.  The message that Steinbeck wishes to deliver to the reader is that there is a larger and more transcendent image of ourselves that has to be appropriated and adopted in order to find and discover real and lasting social change.