Don't know what Nostradamus warned of but in 1917 Our Lady of Fatima said that if men did not repent a worse war would break out and Russia would spread its errors throughout the world.  Many nations would be annihilated and the Church and the Holy Father would have much to suffer.  She said Sister Lucia would receive a sign.  She got the sign and informed the Pope that the greater war was imminent.  The sign was an aurora borealis.  "strange lights" in the night.