Putin’s invasion of Ukraine has put an end to the collaboration between Slavic nations. Russia and Ukraine are the two most populous countries which speak Slavic languages. Their conflict puts an end to the pan Slavic idea: the consideration that different nations were connected by the common root of their languages.
These are the ‘Slavic’ countries

Belarus - 9,498,700
Bosnia & Herzegovina - 3,829,000
Bulgaria - 7,265,000
Croatia - 4,253,000
Czech Republic - 10,200,000
Macedonia - 2,107,000
Montenegro - 621,383
Poland - 38,530,000
Russia - 143,500,000
Serbia - 7,164,000
Slovakia - 5,414,000
Slovenia - 2,060,000
Ukraine - 45,490,000

These countries have languages which are very close and almost mutually understandable. If one translates the word fish into Slavic languages one sees why the pan Slavic idea emerged:

ры́ба (rýba):  Belarussian
ри́ба (ríba):  Bulgarian
rȉba: Croatian
ryba: Czech
ри́ба (ríba) Macedonian
ри̏ба (rȉba): Montenegro
ryba: Polish
ры́ба (rýba): Russian
ри̏ба (rȉba): Serbia
ríba: Slovene
ри́ба (rýba): Ukrainian

Romance and Germanic languages cannot compete with such shared vocabulary.
The pan Slavic idea considered that nations whose languages were close (much greater than romance languages or even Germanic languages) should consider further collaboration. This is why most Slavic countries have flags with three horizontal stripes, blue, white and red. The pan Slavic flag was introduced at the Slavic Congress of Prague in 1848.

The countries considered the Slavic nation more important than religion. Indeed, there are Jewish, Christian, and Muslim Slavs. Moreover, there are two alphabets employed: the Latin and Cyrillic. The pan-Slavic movement overlaps also with the notion of Eurasia, that is the Russian Federation plus the territories of Western and Balkan Slavs.

This pan-Slavic ideal explains an ambiguity in the Kremlin’s attitude towards Ukraine. If they accept to be part of Russia, they are brothers, if they reject it, they are against the notion of Slavic and Eurasian Brotherhood and need to be defeated.

What is striking is that Ukraine uses the Cyrillic alphabet and are Orthodox Christians like Russia. However, the overarching pan-Slavic, Eurasian idea has destroyed any form of contact or collaboration between Ukraine and the Russian Federation in the foreseeable future.

A conflict between two neighbouring countries implies the creation of future artificial trade routes which will avoid the trading partner with which one borders.

If Putin loses the war with Ukraine, he will have no trade with a significant neighbouring country. If Ukraine regains control of the territories it had before 2014, Russia will lose important access routes to the Black Sea.

Pan-slavism, in theory is based on collaboration and friendship. Putin has ended it by invading Ukraine on the 24th February 2022.