וְזֶ֥ה הַדָּבָ֖ר אֲשֶׁר־מָ֣ל יְהוֹשֻׁ֑עַ כָּל־הָעָ֣ם הַיֹּצֵא֩ מִמִּצְרַ֨יִם הַזְּכָרִ֜ים כֹּ֣ל ׀ אַנְשֵׁ֣י הַמִּלְחָמָ֗ה מֵ֤תוּ בַמִּדְבָּר֙ בַּדֶּ֔רֶךְ בְּצֵאתָ֖ם מִמִּצְרָֽיִם׃
And this is the cause why Joshua did circumcise: all the people that came forth out of Egypt, that were males, even all the men of war, died in the wilderness by the way, after they came forth out of Egypt.
Read halakhic rulings (Jewish law) on Joshua 5:4: and classical halakhic sources.