Off topic:How to merge multiple tab-delimitated files

Question

[Dattatray Mongad]

I have several (about 40 files) tab-delimited files for each genome (having k-mer counts). The format is

AAAAAAAAAA  2
AAAAAAAAAC  8
AAAAAAAAAG  2
AAAAAAAAAT  8
AAAAAAAACA  27

I want to merge them. My ultimate aim is to make dataset of kmers of each genome. I have used KMC to calculate kmers.

Any suggestions to use other tools are also welcomed.