Looking back, nothing could have prevented the pandemic, if not China itself in January. Once the virus was traveling, you can’t prevent spread. There will always be countries and people who will not follow the rules.
The lockdown did save lives, but could not do anything else.
Given that contagion to African and South American countries came from Western Europe, at a stage when China already had gained control over the Virus inside its borders, it's not clear that “nothing could have prevented the pandemic”.
It's obviously something that governments who failed to act want you to believe, but it's not definitive truth. Maybe the uncontrolled situation in Iran would have been enough for the pandemic to happen, but travel from Iran is also much less important (in volume and economic consequences) than travel from the US, France or UK, so there's no certitude here.
And again, late lockdown did save lives, but with huge economic cost whereas early lockdowns saved many more lives with only a fraction of the economic cost, people who delayed the lockdown bear the entire responsibility of the additional deaths and economic disaster.
The lockdown did save lives, but could not do anything else.