[Wine] heightens and inflames our passions (generally indeed that passion which is uppermost in our mind), so that the angry temper, the amorous, the generous, the good-humoured, the avaricious, and all other dispositions of men, are in their cups heightened and exposed.
And yet as no nation produces so many drunken quarrels, especially among the lower people, as England (for indeed, with them, to drink and to fight together are almost synonymous terms), I would not, methinks, have it thence concluded, that the English are the worst-natured people alive. Perhaps the love of glory only is at the bottom of this; so that the fair conclusion seems to be, that our countrymen have more of that love, and more of bravery, than any other plebeians. And this the rather, as there is seldom anything ungenerous, unfair, or ill-natured, exercised on these occasions: nay, it is common for the combatants to express good-will for each other even at the time of the conflict; and as their drunken mirth generally ends in a battle, so do most of their battles end in friendship. (5.9.10)
So, as you may have noticed, there is a lot of drinking going on in this book. But while Fielding mostly seems interested in the hilarious possibilities of drinking too much, alcohol also caused huge social rifts during his lifetime in the early 1700s. This subtle association between (a) poverty, (b) social disorder, and (c) booze seems to underlie the narrator's claim that, "no nation produces so many drunken quarrels, especially among the lower people, as England." (We're assuming that, by "lower people," the narrator means working class people. Not, like, mole people who enjoy living below ground.)
What's interesting about the book's approach to this issue is that, instead of finishing off this passage with a lecture—"in conclusion, drinking is bad and leads to fighting!"—the narrator just says, well, most of those drunken fights are friendly anyway. It's all in good fun!