Following are some key events in the history of Zimbabwe:

President Robert Mugabe's ruling ZANU-PF party faces its biggest challenge in 20 years of post-independence rule from the main opposition Movement for Democratic Change (MDC) led by former trade unionist Morgan Tsvangirai. 

1834 - The Ndebele invade from the south and establish the Ndebele state. 

1870 - Ndebele King Mzilikazi is succeeded by his son Lobengula. Around the same time Europeans begin exploring the region, in particular Cecil John Rhodes. 

1889 - Rhodes forms the British South Africa Company. 

1890 - The BSA establishes the colony of Southern Rhodesia. 

1922 - BSA administration ends, the colony's white minority votes to become a self-governing colony. 

1930 - Land Apportionment Act severely restricts black access to land. 

Black opposition to colonial rule grows, leading to the formation in the 1960s of nationalist groups; the Zimbabwe African People's Union (ZAPU) and the Zimbabwe African National Union (ZANU). 

1953-63 - Britains brings together Southern Rhodesia (Zimbabwe), Northern Rhodesia (Zambia) and Nyasaland (Malawi) in the Central African Federation. This breaks up when Britain concedes independence to Zambia and Malawi. 

1964 - Ian Smith of the Rhodesian Front (RF) becomes Prime Minister and leads call for full independence from Britain. 

1965 - Smith cuts Rhodesia's ties with colonial master Britain, unilaterally declaring independence under white minority rule. The move sparks international outrage and economic sanctions. 

1972 - Guerrilla war breaks out against Smith regime; Mugabe becomes leader of the ZANU liberation movement in the mid-1970s after palace coup against Ndabaningi Sithole. Rivals ZANU and ZAPU intensify guerrilla operations from bases in Zambia and Mozambique. 

1979 - Britain convenes all-party Rhodesia conference after escalation of independence war, brokering a peace agreement and constitution for an independent Zimbabwe. 

1980 - ZANU wins independence elections. Mugabe takes office as prime minister on April 18. 

1982 - Mugabe deploys crack North Korean-trained Fifth brigade to crush rebellion by ex-guerrillas of ZAPU leader Joshua Nkomo in Midlands and Matebeleland provinces. Government forces are accused of killing thousands of civilians. 

1987 - Mugabe and Nkomo merge their parties to form ZANU-PF and reach accord that helps end the troubles. 

1987 - Mugabe amends the Lancaster House independence constitution, abolishes post of prime minister and becomes executive president with sweeping powers. 

1998 - An economic crisis marked by high interest rates and inflation, weak currency and rising unemployment provokes riots in January and November and massive support for the Zimbabwean Congress of Trade Unions headed by Morgan Tsvangirai. General strikes paralyses the country in January, March and November. 

Early 1999 - Economic crisis persists, Zimbabwe's military involvement in the Democratic Republic of the Congo civil war becomes increasingly unpopular, Mugabe's land resettlement scheme fails in the courts. 

1999 - Campaign by opposition parties and civic groups leads to Mugabe's appointment of a 400-member constitutional reform commission. Packed with government supporters, it proposes a draft constitution critics say would consolidate Mugabe's powers. 

2000 - Mugabe suffers humiliating defeat in public vote on the draft constitution. Thousands of so-called independence war veterans, backed by government, seize hundreds of white-owned farms, saying the land was illegally seized by colonialists. Talks on land issue with former colonial power Britain soon collapse and veterans accelerate their seizure of farms. 

Mugabe sets parliamentary elections for June 24-25.