All America
1) Is it correct to use "ALL" with a State or Continent?
For instance, ALL AMERICA, ALL ENGLAND, ALL AFRICA, etc,

2) If it's correct, can the expression also be used with the meaning of "all the people" of that State or Continent?
For instance: "All Sweden oppose(s) racism" (all the people in Sweden oppose racism).

3) What about "oppose" in number 2)? Plural or singular?

Question

All America
1) Is it correct to use "ALL" with a State or Continent? 
 For instance,  ALL AMERICA, ALL ENGLAND, ALL AFRICA, etc,

2) If it's correct, can the expression also be used with the meaning of "all the people" of that State or Continent?
For instance: "All Sweden oppose(s) racism" (all the people in Sweden oppose racism).

3) What about "oppose" in number 2)?  Plural or singular?

Answer

Michael has answered well.

I like to read concise English, because it means the person has thought about what they have written. For me, the 'all' is for emphasis if you say: 'The United Kingdom opposes racism' then this is an abstract statement probably of general policy. But does it apply to 'all' of the people in the UK? Regrettably, probably not. Sweden might oppose racism, but does that mean all of the people in Sweden oppose it..?

Answer

In my experience, this usage is less common, more literary and has more impact. It may suit your context quite well. Thinking about it, it only works with singular countries and continents with one-word names like Sweden, Africa, or England.  All+country is still a singular concept.

It sounds wrong to say "All the United Kingdom" - we would need "of", and we would lose any additional impact.  "All the United States of America" could be confusing and would sound strange.