There are a lot of events to keep track of when it comes to these cups - they often reference various events and years. This is meant to be a handy guide to the major events that happened. We take 1895 as the starting point - almost all the items come from 1895 or later. There are exceptions, but they are rare. Here I only list the major conflicts - there are smaller incidents, events, and what not, but those are too numerous to list one by one.
1894-95: First Sino Japanese War 日清戦争. The fighting mostly happened in Korea and ended with the Treaty of Shimonoseki where Japan gained dominance over the Korean peninsula. Taiwan was also ceded to Japan as a result of the treaty.
1900-01: Boxer Rebellion. Often times the cups refer to this as the "Northern Qing Incident" 北清事変. Japan was one of the Eight Nations that invaded China in response to the Boxers siege of the foreign legation quarters in Beijing.
1904-05: Russo-Japanese War 日露戦争. Often referred to on various items as the Meiji 37/38th Years War 明治三十七八年戦, which uses the Japanese imperial calendar to refer to the war. Probably the defining moment in 20th century Japanese history in sending it on the trajectory that eventually led to the Second World War.
1914-15: Japanese involvement in WW1 in China, usually referred to as the Japan-Germany War 日独戦争 or some variant. Japan, as Great Britain's ally (and by proxy allied to other nations such as France, Russia, etc) invaded Germany's possessions in China and Asia, taking over those areas such as Qingdao (Tsing-tao).
1915: Taisho emperor enthronement. By East Asian tradition, the death of the previous ruler has a three year mourning period, after which the enthronement happens, which is why even though the Meiji emperor died in 1912 enthronement didn't happen until 1915.
1918-22: Siberian Intervention. This was an attempt by allies and Japan to overthrow the new Communist regime in Russia. Japan sent close to 80,000 soldiers to Siberia and was involved for quite a few years in the area, militarily speaking. The cups for this normally would normally refer to Siberia シベリア, either as "Siberia dispatch" or "Siberia Victory".
1928: Showa emperor enthronement
1931: Manchurian Incident 満州事変. This is actually a series of events with the invasion of Northeastern China by the Kwantung army that led to the creation of the puppet state of Manchukuo.
1932: Shanghai Incident (January 28th Incident): This is really related to the Manchurian Incident. Japan was basically putting extra pressure on China to try to get more control out of Chinese territories, and a brief hot war broke out in Shanghai. It eventually settled into a ceasefire under international pressure.
1937-1940: China Incident 支那事変. This is sort of the logical conclusion of what had happened in the decades prior - full scale invasion of China by the Japanese army, with the eventual establishment of multiple puppet states. Note that the name used for China here is "Shina", which is now considered a derogatory term.
1941-45: Great East Asian War 大東亜戦争. This is the name applied to the war in Asia after 1941, as the war spread from just China to the rest of Asia.
This is just a simple list of events that are often referenced to by various commemorative items - there are more, of course, but I figured it would be a handy guide if there's any confusion over timing.