Greetings! This question depends on several things. Firstly, what do we mean by global conflict? Below are a trio of possible interpretations with relevant accompanying responses:
- Global in the military sense: In this sense, yes, the First World War was a global conflict. Although the majority of literature and coverage of the war focuses on the trenches of the Western Front or the conditions on the Eastern Front (or even the "lesser-known" Alpine Front between Italy and Austria-Hungary), there were spots of conflict all across the world. The Japanese seized the German Empire's lease of land in Qingdao (Tsingtao) after a brief siege in November 1914. The German East Asia squadron fought the Royal Navy down south near the Falklands Island, and the "Löwe von Afrika" (Lion of Africa) general Paul von Lettow-Vorbeck led a superb guerilla campaign against British and Indian troops in East Africa with a motley force of colonial troops (really recommend further researching this one, makes for excellent stories). Granted, fighting never went as far as the actual shores of North or South America, but in terms of sheer scale, only the Seven Years War (1756 - 1763) compares (and in some respects exceeds) it.
- Global in the political sense: again, a resounding yes here. Though we often focus heavily on the role of the European and American governments in this war, there were parties heavily invested (though not necessarily in terms of active combatant soldiers) in the war. The Chinese Nationalist Government believed that choosing a side would help on the path to ridding China of the western imperialist influence, a wish represented by the dispatching of the Chinese Labour Corps to assist the Entente on the Western Front. In the Middle East, you have likely heard of Lawrence of Arabia's guerilla campaign, most notably against the Hejaz Railway of the Ottoman Empire, in which he managed to gain the support and fighting power of the various Arab tribes who were promised (and denied) an independent homeland after the war. Even Latin America was transformed by the war, with economic effects and political decisions framed by the larger events in Europe.
- Global in the economic sense: this might be one of the "kind of" senses in which the First World War was a global war. I am somewhat restricted here by my utter lack of economics knowledge, but the First World War left massive economic scars in some belligerents, and even elevated others. National economies were harnessed for war, with rationing and government regulation committees such as the American War Industries Board. Even other nations which were not involved in the fighting were impacted by the decline of imports from combatant nations (Latin America most notably).
Hope this brief overview helps, and feel free to ask any-followups as you see fit!
Sources
Dehne, Phillip. "How Important Was Latin America to the First World War?" Iberoamericana (2001-) 14, no. 53 (2014): 151-64. Accessed February 4, 2021. http://www.jstor.org/stable/24368641.
Kennedy, Paul M. "The First World War and the International Power System." International Security 9, no. 1 (1984): 7-40. Accessed February 4, 2021. https://www.jstor.org/stable/2538634.
Howard, Michael. The First World War: A Very Short Introduction. Oxford University Press, 2007.
Pelaez, Carlos Manuel. "World War I and the Economy of Brazil: Some Evidence from Monetary Statistics." The Journal of Interdisciplinary History 7, no. 4 (1977): 683-89. Accessed February 4, 2021. https://www.jstor.org/stable/202887.
Schmitt, Bernadotte E. "The First World War, 1914-1918." Proceedings of the American Philosophical Society 103, no. 3 (1959): 321-31. Accessed February 4, 2021. http://www.jstor.org/stable/985472.