My guess, as a fellow reader, is that the Chileans still discovered gold in the riverbeds of Tierra del Fuego, prompting a desire to establish sovereignty, but the Argentines got a better settlement of the final border. Another possibility is that the Chileans still lay claims that we are not aware of as out-of-universe observers.
Nationalism still exists, but is simply not as powerful, or went along a different path than that of centralization and uniformity found in OTL. Examples range from Italy, where pan-peninsular nationalism is probably associated with the previous Napoleon-influenced Beauharnais monarchy, to Germany, where nationalism tracks closer to the legacy of the Holy Roman Empire and celebrates the diversity of the various German local cultures, from Hungary, where each nationality is considered equal and receives non-land-based autonomy under the Hapsburg throne, to Russia, where the state considers its core peoples to be a 'triune' gestalt of Krasnorossi, Belorossi, and Chernorossi, who despite their differences remain a single group.
Of course, Poles might disagree on this classification of the Belarusians and Ukrainians, as would some Belarusian and Ukrainian subjects of the Tsar.
