The theoretical basis of "workers have no motherland" is:
First, the so-called "motherland" is ruled by the bourgeoisie, a country of the bourgeoisie, not a country of workers.
Second, at that time, Marx and Engels were based on "joint action, at least the joint action of civilized countries, which is one of the first conditions for the liberation of the proletariat". That is to say, Marx and Engels have not considered that the proletariat may first seize political power in a certain country and make itself rise to the ruling class.
Extended data
Engels pointed out: "The situation of the working class is the real foundation and starting point of all contemporary social movements, because it is the sharpest and most explicit manifestation of all disasters in our society at present." The proletariat in China bears the sharpest and most explicit social disaster, and they also shoulder the future mission of the socialist movement.
Great changes have taken place in the working class in China since the reform and opening up. While the traditional working class is becoming increasingly commercialized, rural workers are becoming proletarians, and a large number of intellectuals are falling into the ranks of the proletariat.
In the era of globalization, the expansion of capitalist relations of production in urban and rural areas simplifies "class opposition" and "the whole society is increasingly divided into two hostile camps and two directly opposing classes: the bourgeoisie and the proletariat".