Venezuela has also been estimated to owe $10bn-$20bn to China in debts that Caracas previously paid from oil exports but is believed to have stopped servicing, about $6bn to Russia, and $4bn to development banks” (FT).

Venezuela was allegedly planning to invade a resource rich neighbor before the Trump administration’s actions, as part of a long standing territorial dispute, and I think that was partly so Maduro could keep the support of the population but also partly to deal with the financial problems. So their leaders definitely knew these issues were building up.

Their crude is really only valuable to a handful of countries, the US being the main one. They could really not afford to have worsening relations with the US right as the fracking boom took off.

As their domestic industry shrank, they had to import more and more resources from other countries.