Trench warfare
During the Pacific War, the Japanese used a labyrinth of underground fixed positions to slow down the Allied advances on many Pacific Islands. The Japanese built fixed fortifications on Iwo Jima, Okinawa, and Peleliu using a system of tunnels to interconnect their fortified positions. Many of these were former mine shafts that were turned into defence positions. Engineers added sliding armored steel doors with multiple openings to serve both artillery and machine guns. Cave entrances were built slanted as a defence against grenade and flamethrower attacks. The caves and bunkers were connected to a vast system throughout the defences, which allowed the Japanese to evacuate or reoccupy positions as needed, and to take advantage of shrinking interior lines. This network of bunkers, tunnels, and pillboxes favoured the defence. For instance, the Japanese on Iwo Jima had several levels of honeycombed fortifications. The Nanpo Bunker (Southern Area Islands Naval Air HQ), which was located east of Airfield Number 2, had enough food, water and ammo for the Japanese to hold out for three months. The bunker was 90 feet deep and had tunnels running in various directions. Approximately 500 55-gallon drums filled with water, kerosene, and fuel oil for generators were located inside the complex. Gasoline powered generators allowed for radios and lighting to be operated underground. The Japanese caused the American advance to slow down and caused massive casualties with these underground fixed positions. The Americans eventually used flamethrowers and systematic hand-to-hand fighting to oust the defenders. The American ground forces were supported by extensive naval artillery, and had complete air supremacy provided by U.S. Navy and Marine Corps aviators throughout the entire battle.

Post-1945 to modern day: Trench warfare has been infrequent in recent wars. When two large armoured armies meet, the result has generally been mobile warfare of the type which developed in World War II. However, trench warfare re-emerged in the latter stages of the Chinese Civil War (Huaihai Campaign) and the Korean War (from July 1951 to its end).
During the Cold War, NATO forces routinely trained to fight through extensive works called "Soviet-style trench systems", named after the Warsaw Pact's complex systems of field fortifications, an extension of Soviet field entrenching practices for which they were famous in their Great Patriotic War (the Eastern Front of World War II).
In the Iran–Iraq War, both armies lacked training in combined arms operations. Both countries often prepared entrenched defensive positions and tunnels to protect and supply the cities and bases throughout the regions. Military mobility was drastically reduced; hidden anti-tank mines, and unstable footing made it easy to slide into or get buried in a camouflaged anti-tank trench. Tactics used included trench warfare, machine gun posts, bayonet charges, booby traps, use of barbed wire across trenches and on no-man's land, Iranian human wave attacks, and Iraq's extensive use of chemical weapons such as mustard gas against Iranian troops.
Iraq again attempted to use trenches during the 1991 Gulf War. After the Invasion of Kuwait, Saddam Hussein with the objective of forcing the coalition to engage in costly World War I-era trench warfare, ordered the construction of a massive fortification line in the Saudi-Kuwait border, consisting of regular trench lines, "flame trenches" (ditches filled with oil to be ignited in case of attack), sand berms, trench works, anti-tank ditches, barbed wire and minefields, which became known as the Saddam Line. However, at the start of the Liberation of Kuwait, the US forces charged the Iraqi lines with M1 Abrams tanks modified with minesweeping ploughs and M728 Combat Engineer Vehicles which buried the trench lines, and in many cases, buried Iraqi troops alive. In less than three hours after the initial assault, US and coalition forces had already broken through and bypassed the Saddam line and the rest of war was composed by highly mobile manoeuvre warfare focusing on overwhelming power against the Iraqis.

There was an extensive trench system inside and outside the city during the 1992–1996 Siege of Sarajevo. It was used mainly for transportation to the front-line or to avoid snipers inside the city. Any pre-existing structures were used as trenches; the best known example is the bobsleigh course at Trebević, which was used by both Serb and Bosniaks forces during the siege.
In the Eritrean-Ethiopian War of 1998–2000, the widespread use of trenches raised comparisons to the trench warfare of World War I. According to some reports, trench warfare led to the loss of "thousands of young lives in human-wave assaults on Eritrea's positions". The Eritrean defences were eventually overtaken by a surprise Ethiopian pincer movement on the Western front, attacking a mined, but lightly defended mountain (without trenches), resulting in the capture of Barentu and an Eritrean retreat. The element of surprise in the attack involved the use of donkeys as pack animals as well as being a solely infantry affair, with tanks coming in afterwards only to secure the area.
The front line in Korea and the Line of Control in Kashmir between Pakistan and India are two examples of demarcation lines which could become hot at any time. They consist of kilometres of trenches linking fortified strongpoints and in Korea surrounded by millions of land mines. The Indian Army has fortified the LOC with 900 fixed tank turrets. The borders between Armenia and Azerbaijan amid the ongoing Nagorno-Karabakh conflict are also heavily fortified with trenches and barbed wire, with the two sides regularly trading fire.

Russo-Ukrainian War: In the Russo-Ukrainian War, to safeguard and assert their territories, both Ukrainian and Russian proxy forces have resorted to digging small trench networks and engaging in warfare somewhat akin to the trench fights of World War I in some aspects. This involves soldiers spending extended periods within trenches, employing cement mixers and excavators to construct tunnel networks and deep bunkers for added protection. After the Minsk peace agreements the front lines did not move significantly until the 2022 Russian invasion of Ukraine, as both sides dug elaborate networks of trenches and deep bunkers for protection and the two sides mostly fired mortars and sniper shots at each other.
The 2022 invasion also saw the construction of trench lines and similar defensive structures by both sides, especially after the end of the initial Russian offensive, resulting in a static war of attrition with slow advances and artillery duels, especially in Donetsk Oblast. Pictures of muddy trenches, stumps of charred trees in a shell-pocked landscape made the Battle of Bakhmut emblematic for its trench warfare conditions, with neither side making any significant breakthroughs amid hundreds of casualties reported daily. Modern technology has adapted to the trench warfare, and use of drones and mobile networks is common. The battlefield has been described as "World War I with 21st-century Intelligence, Surveillance, and Reconnaissance".

Cultural impact: Trench warfare has become a powerful symbol of the futility of war. Its image is of young men going "over the top" (over the parapet of the trench, to attack the enemy trench line) into a maelstrom of fire leading to near-certain death, typified by the first day of the Battle of the Somme (on which the British Army suffered nearly 60,000 casualties) or the grinding slaughter in the mud of Passchendaele. To the French, the equivalent is the attrition of the Battle of Verdun in which the French Army suffered over 380,000 documented combat deaths.
Trench warfare is associated with mass slaughter in appalling conditions. Many critics have argued that brave men went to their deaths because of incompetent and narrow-minded commanders who failed to adapt to the new conditions of trench warfare: class-ridden and backward-looking generals put their faith in the attack, believing superior morale and dash would overcome the weapons and moral inferiority of the defender. British public opinion often repeated the theme that their soldiers were  "lions led by donkeys".
World War I generals are often portrayed as callously persisting in repeated hopeless attacks against trenches. There were failures such as Passchendaele, and Sir Douglas Haig has often been criticised for allowing his battles to continue long after they had lost any purpose other than attrition. Haig's defenders counter that the attrition was necessary in order to cause attrition in the German army.
The problems of trench warfare were recognised, and attempts were made to address them. These included improvements in artillery, infantry tactics, and the development of tanks. By 1918, taking advantage of failing German morale, Allied attacks were generally more successful and suffered fewer casualties; in the Hundred Days Offensive, there was a return to mobile warfare. However, if both sides have comparable equipment, capability, and conditions, the trench is still seen in modern wars.