I was curious if two populations are in Hardy-Weinberg Equilibrium (HWE), and if they are merged, then what happens? To find out, I considered populations from the 1000 genome project data. For example, at first, I considered the genotypes of the American (AMR) population from a specific SNPs and checked whether they were in HWE and found that they were. Then I selected the East Asian (EAS) population and found that the genotypes were also in HWE. However, when I merged the genotypes from both populations and checked HWE, I found that it was not in HWE. Surprisingly, when I added 50% of genotypes from each population, they were in HWE. So, I did it for different combinations, for example, 80% genotypes from the AMR population and 20% from the EAS population and vice versa, and found that they were also in HWE. I used the chi-squared goodness of fit test and the Haldane Exact test. The allele and genotype frequencies for each combination are different from the initial populations. What conclusion can I draw from my findings? Should I check to see if there are any assumptions about the test that are violated?
As @Domen points out, there is no expectation that adding two populations that are each in Hardy-Weinberg equilibrium will initially create a new population in HWE.
OP's procedure of combining different proportions of the initial populations, then checking for HWE, is essentially like asking how much of one population can be added to another before HWE is lost. This vaguely gets at the question of how different the two populations are to begin with, but doesn't provide any information on whether the assumptions underlying HWE are met.
A better function to ask about the initial difference between populations, and that can be calculated from the initial allele frequencies, is the fixation index, FST.
Incidentally, if the assumptions of HWE are still met after the two populations are merged, then after one generation of mating HWE will be reestablished across the whole population.