Original quote
Culinary fusion is all the rage; more novels translated from
languages then ever before, although few are read, and in the surest
sign of cultural globalization, football, finally has reached America.
- italics signify the subordinate clause
The preposition in
shows that the main clause, Culinary fusion is all the rage
and the second main clause, the surest sign of cultural globalization...
are connected, through the co-ordinating conjunction and
:
Culinary fusion is all the rage; more novels translated from
languages then ever before, although few are read, and in the surest
sign of cultural globalisation, football, finally has reached America.
The role of co-ordinating conjunctions is to connect main clauses together but can also co-ordinate 2 noun groups—I think the 2 overt nouns it’s connecting is “culinary fusion” and “cultural globalization": “Culinary fusion is all the rage and [in the surest sign of cultural globalization * ]…”
- With football entering America as a marker of cultural globalisation.
Therefore, in this case the preposition is expressing a condition. The condition being that [cultural globalization such as football entering America] are all because of culinary fusion (the overarching 'theme').
The preposition almost ensures that "Culinary fusion" is the antecedent to "cultural globalization" and "football" that the co-ordinating conjunction does not. Although, co-ordinating conjunctions can coordinate 2 or more noun groups -- they don't necessarily signify that the nouns are related to the other.
Compare 1 and 2:
(1) Culinary fusion is all the rage and the surest sign of
cultural globalization, football, finally has reached America.
(2) Culinary fusion is all the rage and in the surest sign of
cultural globalization, football, finally has reached America.
In (1) it's obvious that "cultural globalization" is antecedent to the noun "football" but is not necessarily a result of culinary fusion. They are almost read as separate points because of the conjunction between them. In (2) it makes it much more obvious that culinary fusion and football entering America are connected.
ODO lists this definition of in under sense 4:
(often followed by a noun without a determiner) expressing a state or
condition.
(3) ’to be in love’
(4) ’I’ve got to put my affairs in order’
(5) ’a woman in her thirties’
The condition of (3) is an object of desire, the condition of (4) is “my affairs” will only be “in order” once I put them so and the condition in (5) can be construed as a statement which is subject to change: at present, she remains “in her thirties”.
Though omitting the the preposition would be fine that would depend on what you want to convey. So the use of "in" is extremely important here and removing it would change the meaning of the sentence altogether.
Research has shown that "preposition ellipsis" is common in everyday speech and in some prose:
What are you doing (in) here?
A non-fiction titled "Do the Right Thing" published in 1998 has this
sentence: 1
Am I treating this stranger with the same consideration that I
would (with) a friend?
In these cases, adding the preposition is unnecessary and omitting the preposition does not change the intended meaning of the sentence.
1 https://english.stackexchange.com/questions/195724/when-do-you-leave-out-the-preposition-in-a-relative-clause