It seems like all the current Spanish speaking countries spoke Spanish and were thus conquered by the Spanish long before the american colonies came, unless I'm mistaken.
It just seems like there would have been a shitload more Spanish speaking allies from all those countries fighting together to save/conquer America (USA) for their own rather than let the English speaking armies take it.
Why didnt or weren't they able to do it? Why is Spanish not THE dominant language?
By the world I assume you mean the Americas.
Spain's voyages of exploration were the first to "discover" the new world (if you don't count the Viking who failed to establish successful colonies). While there were great empires in the Americas prior to Columbus's arrival, they were completely devastated by European diseases (smallpox etc.) It is estimated between the arrival of Columbus and the conquest of the Aztec's and Incas that 90% of the population of the Americas died of European diseases. This made it easy for European's to establish colonies in the Americas. Cortes conquered the Aztec Empire establishing the colony of New Spain (modern day Mexico) and Pizarro conquered the Inca's establishing the Spanish main (modern day Peru). Portuguese ships a atempting to round the tip of Africa and landed in modern day Brazil establishing Portuguese colonies in there. Britain colonized the east coast of the North America and France had Quebec and a lot of open land in modern day USA.
This left Spain with a vast empire including basically all central and south America apart from Brazil. They became the dominant world power of the 16th century. The Spanish monarchs were not very good with economics and Spain experienced rapid silver inflation and this coupled with overspending and just bad luck (Spanish Armada) caused Spain to go bankrupt in the early 17th century.
This started the decline of the Spanish Empire. The Spanish supported the Americans during the American war of independence but did not recognise the independence of the USA after the war. Then in 1803 during the Napoleonic​ wars France sold Louisiana to the USA. (This area was given to Spain after the Seven years war but taken back by France in 1800).
Most of Spain colonies became independent in the early 19th century. This was kicked off in 1808 when Naploean for whatever reason decided to invade his ally Spain and imprison the King. This lead to conflict in the Spanish colonies. In the next few decades South America became many different independent countries.
Now back to USA. In 1848 the a newly independent Mexico came into conflict with the USA over Texas which ended in USA annexing most of Northern Mexico all the way to the Pacific.
The Spanish American war in 1898 was fought over the remaining Spanish colonies which were all islands which ended in America taking Puerto Rico and the Phillipiens.
In the end, when Spain was powerful enough to conquer North America it was more focused on invading Britain and sent several Armadas to invade but all but one failed because of weather. In theory if the Armadas were successful Spain would have taken the British colonies in the new world.
TL;DR The Spanish Empire in America and the USA only co-existed for a short time.
Before I try to answer this (Can't promise anything), are you asking why the Spanish didn't settle in northern America or why they didn't try to attack it after the english-speaking northern colonies were formed?